1.Not if reasonable taken care of them other wise I would not have a collection of 30 to 50 yo regs in prefect working order. The insides of my 1958 DAAM look like new. I restore vintage regs as a hobby so I spend a good bit of time with very old regs. We are talking about rental stuff, I understand that you look after your kit and it will last 100years, not the case with rental kit.
2. Right, and these are replaced during a normal (proper) service.
3. You still have not told me what parts go bad that are not replaced during service. Yokes don't bad, main bodies don't, end caps don't, pistons don't, springs don't, balance chambers don't.....what am I missing that wears but is not replaced as part of a normal service??? All parts if not cared for will degrade. Is this not the case?
Maybe I was a little unclear, what I ment was if I can get a used car (in that case but it holds for regs as well) that had all the major operating equipment replaced in it and it was being sold for 1/4 the price of a new car I would buy it. Scrathes on the paint or stains on the seats do not keep it from running, same holds true for regs. The fact is that springs, pistons, chambers (aka engine & transmission) is not going to be replaced new as per your statement and then sold at a 1/4 of the price.