We took an older 4bt unit out of service at work at 60k hours, the power head went bad. This was the last 4bt unit we had in the fleet, all of the others ended life at about the same service level and all were for the power unit going bad, none for the engine having a failure. They had your typical maintenance on them for a construction generator, we try to change fluids at 250 hours but they sometimes go longer than that, usually never more than 500 hours though.
I tried to buy the last one that they had, but it went to an auction house and someone paid 2500 for the unit, more than I was willing to pay for a 60k hour 4bt and bad power head.