We, too, had problems with leakage on our new 1998 2619. Our dealer tried to repair it with a new slider valve. After a couple of more problems that I tried to fix myself, one of the customer service reps asked me about the location of the plastic locator disc. He described where it was supposed to be, and my installation didn't have one. See the directions below, and look at the diagram at [
http://www.thetford.com/permanent_el...icservice.cfm] item #5 of the instructions (repeated below).
Place unit on closet flange and locate position for plastic locator disc by tracing around one of the front legs. Drill 5/32" dia. hole in floor and fasten disc to floor with flat sides oriented as shown. Use #10 screw provided. Important: This disc prevents toilet from moving on floor.
If you are having difficulty, try moving your toilet with a twisting motion. If it moves a 1/4" or more, your unit is missing the locator disc.