I have a W33, so my experience may or may not apply to you. Probably won't as your problem seems slight different, but here it goes...
I found a replacement for the OME impeller at half the cost. Was the same size measured with digital calipers. The only difference was the dang key / shaft. Westerbeke
appears to have made a custom fitted key so they can screw us on the pump and impeller. No matter though as I was able to push the key out of the old and place it into the new.
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