It isn't just Dometic,My Thetford had the same problem. Not caused by winterizing,we don't have to do that in Sunny So Cal.:B
Cheap plastic valve and a small leak that wasn't discovered until I saw a small puddle. Thought it was a bad connection but on further inspection I found that it was leaking thru the side of the flush valve.
It is a good thing to check now and again. One thing nice about the Thetford the valve was easy to replace,just unscrew it and pop the other one in,no need to pull toilet.
