I had to replace my Thetford valve over the winter and saw a lot of silicone on the EZ slider valve itself, but not nearly as much as you had on your floor gasket. Because the installation manual said nothing about using silicone I decided not to reapply it, and things have been fine for six months.
My silicone was not the cause of the toilet problem, by the way - it was a valve gasket slippage.
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