As the former owner of two John Deere backhoes, I'll tell a bit about my woes:
In 1999 I bought a 1974 JD 410. It was low hour, joints tight, no welds on it at all. Factory rear bucket had a crack in the cutting edge. Front bucket had a crude job of adding to the weld on cutting edge. Overall, even the original paint looked good. It had just sold at a farm auction. I was considering buying it from the new buyer. I vaguely knew the farmer who had sold it. I asked him if there was a reason I wouldn't want it. He went on about how good the brakes were.
I tried to drive it home, 10 miles. I ran low on hydraulic/transmission oil. Had to get oil to refill it to get home. Resolving the leak, it ran fine first hour, then didn't have enough power to lift an empty bucket. Loader took 2 minutes to raise to full height.
I went to my nearest John Deere dealer, found they were closed.
John Deere now has one dealer in my state, 65 miles away from me. They offered to send a mechanic, He would not have hydraulic diagnostic tools, only a good mechanic. He MIGHT be able to diagnose the problem. His trip would cost between $1200. and $1500. Most wanted me to try a new hydraulic pump $1400. The pump on it was a different color, I figured someone had already done that.
I made some calls, tried to figure what the problem was. Somebody several states away said I had an oil flow problem. Oil was flowing somewhere it shouldn't. Get an infra red camera, start it up cold. As oil starts to warm, it'll show heat where oil shouldn't flow.
Tried that, found oil was slipping past in two sections of the backhoe valve. New Hampshire Hydraulics confirmed the diagnosis. They believed it was defective when new.
John Deere said the part was No Longer Available.
New Hampshire Hydraulics said they couldn't get the two sections I needed, but a whole different valve could be assembled from parts. It took 6 months for them to provide the valve. It cost $1400. New valve was 1.5" narrower than the old, so joystick controls wouldn't mate up. I fabricated a new joystick mechanism.
20 years later I bought a JD410C from a friend. Backhoe boom wouldn't lift when warm. When it was up, it sagged in seconds to the ground. John Deere Parts & Service offered no help. The port relief valve size of a 1/2" hex socket was unavailable. After weeks of trying every lead possible including the dealer several calls, I asked to speak to the service manager. I posed to him: "So your telling me your best customer had my problem, there is nothing you could do for him?"
No he said, "We can rebuild it."
$48. I had a rebuild kit, after hours spent trying to find this thing. Turns out an identical port relief valve different part number is available, just have to readjust relief pressure.
I have found John Deere is unconcerned about older machines, and their owners.