I agree with Trikepilot.... as long as the service records can be produced, I wouldn't worry about it. I've heard on this site (RV.net) that Onan's can go 20,000 hrs. before a major repair service.
I run our Onan 10K diesel almost monthly for exercise and in the summer while going down the road for roof air. We have just over 500 hrs. on it now in 7 years.
About the crack, I would check to see how much it would cost to replace and knock it off the price as I would want a new shower stall.
MM.
Mr.Mark
2021.5 Pleasure Way Plateau FL Class-B on the Sprinter Chassis
2018 Mini Cooper Hardtop Coupe, 2 dr., 6-speed manual
(SOLD) 2015 Prevost Liberty Coach, 45 ft, 500 hp Volvo
(SOLD) 2008 Monaco Dynasty, 42 ft, 425 hp Cummins