Sea Water Pump Rebuild on Yanmar 3JH2E

I am attempting to rebuild my raw water pump (Cooling Sea Water Pump #129573-42502). I have removed the pump from the engine, removed the impeller and have been able to remove the circlip and the mechanical seal stop ring. I have pressed the pump shaft out of the housing which came out fairly easily. The shaft and bearings look fairly free of wear. My manual indicates that I should remove the impeller wear plate so I can remove and replace the mechanical seal. Okay, so how do I remove the impeller wear plate? It is a flat silver colored plate in the floor of the impeller compartment. It has a central hole that the pump shaft fits through and two other small holes through the body of the plate. I don´t get it, I cant even get this plate to move. Is there some sort of trick to removing this plate? The manual just says remove the plate. There must be more to it than this. HELP!