Yeah as someone who runs only junk, working on tired iron isn't fun. Having to depend on tired iron to preform is even worse.
Worst feeling in the world is having a truck waiting to be unloaded and a machine deciding it's a good time to take a rest....
That being said, once the bugs are all chased out, it can be dealt with, just depends on your use. Case in point, my Hyster. I got it for a very good price, but it was sick. Lift cylinder had to be repacked as did the steering cylinder and it needed new tires.
Figured out how to repack the cylinders myself, and lucked on to some truck tires that would fit the machine (they are bit light, but serviceable), did fluids and filters and it worked.
It's still got it's issues; I still need to fix the parking brake, it's got no seat and sometimes if you try to just shove it in gear it gets suck, simple matter to just pull the shifting lever, take a big screwdriver and move the gear box to neutral. But over all it's a solid old lift.
All fine and good and pretty much the only way a gobber like myself would have a 25k forklift, but would not work for someone moving stuff around day in and day out.
If I were buying used, I'd buy as big as I could, (more room to work on it and bigger machines just take more abuse) and I'd want one with a standard transmission. They really are simple machines, not much too them, just lots of iron in a small footprint.
Here's mine, that's the heaviest thing I've picked up with it, about 17,000lbs at a 48" center or so.