About two years ago, the hydraulics on my 1973 John Deere 1020 diesel quit working. Loader control valve was leaking, and I've been told they aren't rebuildable, and I couldn't find a replacement that would work, so I removed it took it to a local hydraulics shop. They determined it wasn't worn out, so just replaced seals and O-rings and it worked fine (tractor has about 2000 hours on it). Then, the hydraulics would fail completely and intermittently, so we called the local JD dealer. Pickup and delivery were $90 per hour from the time they left the shop until they got back.
Well, the fuel tank was leaking and the radiator was worn out, and the seat was completely gone, so we were into repairs almost $5000 before they even started working on the hydraulics. After splltting the tractor, they found out that three bypass valves had been replaced, and apparently, the cages and ball bearings had broken and worked their way through both the feeder pump and hydraulic pump, ruining both. (BTW, I had had the tractor for 25 years, and I didn't replace the bypass valves, so it took a long time for the parts to work their way through the system.)
More than two months later, they brought the tractor back, and the total bill was just under $15k. Thank goodness we had just sold my business and building so we didn't have to borrow money. In the middle of this process, we talked to the salesman about trading the 1020 and buying a new tractor. They didn't want to do that because they would have a $5000 tractor to sell (I could probably get $10k for the tractor because it's a diesel (fairly rare) and has low hours. Still we have $15k in and $10k tractor. AND, the new tractors we could find were about $25k, and had half the power and lift capacity the 1020 has. (The head mechanic whispered to me - "They don't make them like this any more".) And it's true, the new ones have plastic hoods, emissions controls, and all sorts of electronic crap that they weren't using in 1973. The head mechanic is a friend of my son's and discounted the labor and removed a bunch of miscellaneous charges, as much as his boss would let him.
Anyway, now we have a 45 year old tractor that works as new. We were kind of stuck between a rock and a hard place, so the best way out was to hang the cost and fix the old tractor. A comparable new tractor would have been around $40k.