Looked at a friend's old 717 today....used when he bought it 16 yers ago. The oil whiper is starting to go, can see that it's getting ragged and shedding bits, but so far it's not clogged the valving.
Have an old 777 that is proably about as old...call it 22 years...a couple of years ago, the oil whipe just fell apart and the gun would "hissss" from the muzzle as you pumped it. Took it apart, cleaned it, but didn't have a replacement oil whipe. A cut length of new tennis shoe string, over lapped twice, fit the recess fine...didn't bind...holds ans spreads oil....and has been working great for the last couple of years.
So...from two of mine and a look at a couple of others, looks like something between 15 and 20years.
The only other things seen often are (1) ham-handed people over tighten the screws and strip them (2) teh grips tend to crack when the grip screw s over tightened and (3) broken plastic sights from being dropped or miss handled. Figure these don't count as the owner had to do soemthing worng for a problem to arise.