I just wanted to check back and post my results. I got my gasket, replaced it, vacuumed the sand/silt to waste, and everything's working great. After replacing all the gaskets in the multivalve an putting magic lube everywhere, the handle moves so smooth and feels brand new. The old gasket just came right out. When I bought the house back in 2004, I had the pool company come out, open the pool, and show me how everything works. They replaced the gasket then but I don't think they even used any adhesive. It just came right out. So, my pool is clear and no more sand/silt is coming back in during backwashing or any other time. Thanks for all the comments and help.