Slow leak in tire sidewall

On my 1996 L9000 one of the drive tires has cut in the sidewall about 3/4 inch long. It seems to only leak if it's on the bottom when I stop or load. I only use the truck on my own property at less than 20 MPH. The tire is a retread but has better than 60% tread and there doesn't appear to be any cord damage. Is there anything I could try to stop the very slow leak in the sidewall or will I need a new/used tire?

I would patch it on the inside then if the hole is very big on the outside i would put a patch there to. They say never patch a side wall and i never did on a customers tire because of it flexing but i have done some for my self and never had a problem. I was hard up for tires one time and found a pair one had a patch on the sidewall out side . I ran it along time and never had a problem. I also cut a rear tire on a tractor between the lugs i booted it and put a patch on the out side . That patch held on till the tire wore out. They have patches to use on the out side.

You could try slime if you didn't want to even go to the trouble of breaking the bead. That tire will be "aged out" of safe and legal road use, not to mention it's already disqualified by a sidewall leak, so nothing to lose. It might mess up the rim, but rims are easy to find.

A quart of antifreeze may help. I'd probably just put a plug in it.

Thanks for the suggestions.
I was thinking maybe a plug. I've plugged a sidewall on my pick up 1 time just to get it to the tire shop about 5 minutes away. I'm sure I'd have to drill the hole bigger so I could get the plug in. I don't want to try and break the bead or get the tire off the rim. I thought of using a patch made for the outside but don't think it would work on tire that gets a lot of flexing and is higher pressure.

Runout casings average 55 to 60 bucks with 4/32 left, better off to find a runout.

I'm not sure if I have the right tools to get the wheel off and don't know how difficult it is. I thought about a used tire. The truck isn't registered. I could maybe get an in transit permit for insurance to take it to a tire shop for repairs. I guess I could try a plug and if it didn't work then go the used tire route.

Truck tires are not as hard as you'd think to break the bead and change with hand tools. If it's an outer, and a plug doesn't work, then you could break the bead on the truck, and pop the outer side off to patch it from the inside. If you add slime, no chance of patching it, but hopefully you wouldn't have to.

It is on the outside. I called 1 commercial tire shop that I've had good service from but they don't sell used tires. Another commercial tire shop sells used tires starting at $200 and $38 to change over. I also called a heavy truck wrecker fairly close to my land but the guy was was really grumpy on the phone. I asked about a used mud flap and a tire and he said they don't keep track of what they have. He said he's sure they'd have a mud flap but couldn't give a price. He asked what a new one is worth but I didn't know. I'm sure they'd have a used tire probably on a rim but are just miserable. They have a few reviews saying the same thing so I'd rather not deal with them. I'd only need a mud flap if I drove the truck somewhere but it doesn't look like my current insurance provider will provide insurance if I got an in transit permit. The permit is $24 which is OK but you also need the insurance. Probably much easier to just take the wheel off.
I think I'll try the plug and see how it goes.

Have you went over it with soapy water to ensure that it is the cut and not around the valve stem or somewhere else if the cut ends in a hole a plug will hold in the sidewall fine for OFF ROAD use
I really like these blackjack plug kits and use them quite often on semi tires the have different length and thickness plugs https://www.amazon.com/BLACK-JACK-T...ocphy=9020110&hvtargid=pla-583155367190&psc=1

A sidewall patch would usually work fine for small hole like that but again would be for off road use only so you would have to do it yourself

Just as a note if the tire was in good enough condition and generally less than 10 years old a side wall hole can be sent in for spot or section repair then vulcanized restoring it to roadworthy condition with the exception of steer position

A used casing would probably cost as much as purchasing a buffer wheel, can of cement, a box of patches & a stitch wheel.

It's definitely leaking at the cut. I could hear a slow hiss when the cut was on the bottom after loading the truck with clay. When the cut is at the top of the tire the leak was so small I couldn't hear or feel it. The tire is pushed out very slightly where the cut is. I put a little rubber cement on the cut and it showed a tiny hole in 1 spot. My plan is to put a plug in with a liberal amount of rubber cement for tires. I think it's actually vulcanizing fluid from looking online. I'm sure I'll have to drill the hole bigger to get the plug in. I'd let the plug and cement dry for a while and then cut the plug fresh with the tire. Then I'd scuff the tire and put an outside patch on mostly to protect the plug than to hold air pressure. I watched a video where someone actually cut a piece of sidewall from an old tire and glued it on the outside of an off road tire with a slash on the sidewall. I have hundreds of old tires for putting around the oval track so was thinking I could do this too. Because it's a Dayton rim I could put a small ratchet strap around the tire to put a lot of pressure on the patch and leave it on for an hour or so to be sure the cement fully dried. I'd taper the sides so they're less likely to snag on something. Pretty redneck repair but if it held air would save a lot of hassle.
One thing I'm not sure about is how hard is it to remove one side of the tire from the rim while still on the truck? I think I could break the bead by pushing on it with the skid steer bucket against a wood block or piece of steel. Would it be easier to remove than an 8 or maybe 10 ply skid steer tire? I have a couple short tire irons and a longer pry bar to use and some good tire goop. Just wondering if it's worth trying to get a patch on the inside or try the plug from the outside first and if it leaks look at doing something different?

I'd try it from the outside first, whether that's slime or a plug. personally wouldn't bother with a patch on the outside, it will last fine without one if it seals, and if it doesn't seal, the patch won't hold. If a plug doesn't work, try to break the bead. Use soap to pry the bead over the rim, murphys oil soap in water in a spray bottle. Little bit at a time, don't get greedy, push the opposite side into the recess, or do it when you have a stronger helper around.

What size is this tire, 24.5? If so it's hard to find 24.5 used or new right now. I sell low pro 22.5 runouts
for $60 {casing credit} when someone comes around needing one.

How long has that tire been mounted? I've seen older tires where the tire adhered to the steel rim, and wouldn't come off for love or money. Then you have to cut the bead wires with a sawzall and work from one cut end.

It's an 11R 22.5 tire. Being a good retread I'm pretty sure they were put on the truck before it went to the auction in late 2016. The front tires were new Bridgestones but a different size, maybe low profile.