I have a 1989 C-34 with M-25XP engine. Last season I got tired of dealing with the old Sherwood pump and changed to the Oberdorfer M202M-837/908 (Depco). The impeller failed just as you have described after only 10 hours of operation. I replaced the impeller with a replacement that I had purchased at the same time as the pump and it was also defective. The next replacement lasted the rest of the season. I think they must have had a manufacturing issue but there may be a lot of those defective impellers out there.