It really all depends on alot of factors. How well the machines have been maintained, plays an important role. I have had Cobe C3's with 35,000 hours that were still reliable and have had ones with 17000 hours that were problematic (due to neglect). Anything can be maintained and repaired but in general anywhere from 7-9 years or approximately 30,000 hours and it's time to start budgeting for new equipment.
We have C3's with 60,000+ hrs and still running strong. With proper and routine maintenance these machines continue to operate extremely well. Although as in the previous reply we also have a couple of low hour machines that tend to require a bit more work.
