Thetford dump valve

Has anyone had issues with the Thetford dump valve? I use only Thetford products in the toilet ands still have to replace The dump valve every 2 years at $40.00 a pop. Thetford Customer Service is useless, They have no cue on these toilets. We've gotten so good at changing them out I now can do it in 15 minutes! The valve feels like it's pushed in all the way, but it takes longer to charge and the tell-tale whoosh isn't there when you pull the toilet valve.We use our TM this past weekend and sure enough the valve was screwed up. The rubber doesn't allow the slider to close completely.

Thanks

Mikeyy1953