The three most common old equipment failures are:
1. Its old.
Things wear out and techs are not incentivized to work on old junk because its going to fail again probably pretty quickly.
2. Refrigerant Leaks
Its old, old pieces of metal that are constantly in contact with moisture corrode and literally disintegrate.
3. Physical Damage
Its old, and its been pissed on by your dog 10,000 times.
But if its fixable and I think it can be done relatively cheaply, I will be glad to repair any system even if its older than I am. Im lazy and replacing units is alot of physical labor and time that I would rather spend golfing.