A well maintained 12 kw diesel gen at 1800 rpms may only last 10,000 hours if ran at no load. It "may" run 20,000 hours at continuous half load. Or the same at full load. No one here is gonna wear one out in any case. Lack of use kills most of them.
That is a great question Hawg asked. Am I to assume that your reverse cycle heater uses raw water for a heat sink/source as opposed to air? I was on a newish boat the other day that had a reverse cycle (heat pump essentially) that used air as the heat sink/source. I know they would not serve my purposes, but a system that used raw water would work pretty well most of the time. I can get ice in my harbor during really cold spells (fresh water streams feed into the harbor near my moorage) but most places the water temps stay in the high 40s in the winter.
Yes, the reverse cycle takes heat from the raw water.