We have a Thetford Aurora toilet.  We had difficulty flushing, as though the ball was sticking.  As per troubleshooting, we sprayed it with soilicone.  This helped but for shorter and shorter periods of time.  Now the ball will not move at all when the pedal is depressed, but the water still runs and fills.

We had the same problem with our 3 1/2 year old Thetford and was told that the cost of dismantling and repair would be about the same as a new toilet. so we got a new, better model for $225.