Has anybody ever known of an oberdorfer pump wearing out? I have a 1983 M25 with an orberdorfer pump. The water pump was working ok, but when I change the impeller it doesn't pump. I put two new impellers in and neither one works. The old one is too worn to run for another season so I need to address the issue. I sanded the cover smooth and have run test by poring water down the inlet hose watching what comes out of the end of a discharge hose taken off of the heat exchanger. I have seen some water movement doing this, but nothing like what i would expect. I'm thinking that the inside of the casting could be worn out and preventing the impeller from working properly.