I don't put a lot of value on being able to swap buckets quickly...yes, it is nice to have x-change, but I am good with bolt on bucket (ironic, but PO removed x-change from my machine - he said it got sticky and was a hassle). It only takes me a couple minutes to swap buckets. You get good at it.
Notwithstanding the fact I like Bobcats, the 4000hrs on JD is too much. Unless everything has been swapped out, I wouldn't even go near it. Too many hours no matter how well it was treated. The pump, two drive motors, the swivel and swing motor, plus the engine will likely need an overhaul or replacement.
Plus, the BC has power to burn relative to JD and most other machines in weight class. You will use slightly more diesel as a result, but won't lack power.
Odd, the JD specs have it being slightly heavier, yet, 25% less hp.
I so agree about having a thumb and a cab....if I had to choose, thumb is more important, but it depends where you live. I'm north of 49 and a cab is a must also.
I rib my fellow mini-excavator friend about his machine...no thumb. Imagine using your hands without your thumb...that is the difference. Huge, especially if moving rocks or trees etc.
I wouldn't get too caught up in the mechanicals, but I would check the bushings - have arm off ground, and give the whole works a shake side to side. You will get slop, but a lot is a sign that it had a breaker/compactor on it, or the person failed to grease it regularly, and/or was working in gritty material. Bushings are a pain to replace. Rollers, idlers and tracks, no biggie. The house should be checked to see the bearings are tight. Lastly, the engine...clean coolant, and black oil with no shiny crap in it. Some folks get the oil tested. As long as it sounds good (if you play around diesels, you'll know a good sounding engine), and is clean, they can putter for a while.
I made up a skookum pressure tester which I would plug into machine and check pressures....would tell me a lot about it's health.
Finally, a machine with a maintenance record or a stack of receipts showing maintenance is a good sign...if I see hodge podge repairs, I'd run.
Ironic, but when I got my machine, it looked like hell on the outside, but I open the engine and hydraulic compartment, and it looked spotless (near new). Owner (a stickler for maintenance) lent it to friend (real estate guy - go figure) who flogged it, but the hydraulic components were sound, as was the engine. That's what sold me. I've replaced 5 rollers and 1 idler....no biggie (and redid front end bushings - pricier than I thought and took finesse to swap them out - more money than all the idlers and roller I replaced). I've put a thousand hours on it, and hopefully, can put another thousand on it before I need to worry about big ticket items like drive motors.