Had a similar situation with a '94 Bounder Shurflow water pump. A couple of the case screws were showing signs of rusting so I took the entire thing apart, cleaned it all out, and there was some crud here and there, but not too bad. Used Vaseline to lube the odd shaped rubber gasket they used around the pump, sort of a cloverleaf style gasket I knew wouldn't be something I'd find at Home Depot so I was really careful cleaning it.
Put it all back together with new SS screws and all was well. No more leak. Still working with no leak 4 years later when I sold the RV.
Here's a link to my blog post about it:
Water Pump Repair