I needed to attempt to repair some leaks on the Thetford toilet. Although an unpleasant task, I removed the toilet, opened it up, and cleaned out the build up inside the tank. Found most of the seals (main housing, EZ slide valve, flange seal) needed replacing. Also there is a "flap" at the exit point on the bowl which is called a vinyl skirt, which is simply a vinyl tube attached with a rubber band and weighted around the bottom to act a a closing flap. Mine was deteriorated and had been allowing smell back into the cabin.
I searched the internet for quite a while, and stumbled on a company in England that sells individual parts for Thetford and other products, right down to separate screws. It is
www.bradtech.ltd.uk. The site setup, ordering procedure, and service is excellent! I live in Canada, and they ship to North America, Europe, and Australia using postal service...somewhat slower but economically reasonable.
I did try the Thetford site based in the U.S., and while they do provide parts, they package them together and found I would be paying a lot of money for a lot of parts I didn't need.
The cost of a new toilet was over $600.00 Canadian. i was able to get the toilet operating like new for under $100 (including the cost of shipping from England).