I replaced the ball seal on my Thetford Aqua Magic Style II toilet. When you order a ball seal kit you will also get a replacement waste seal. You will get a waste seal with every kit you order. I ended up with three new waste seals.
I removed my toilet and I did a complete rebuild. My water valve and ball valve seals were leaking so I replaced my water valve seal, my ball valve seal, my vacuum breaker, and my waste seal.
My only problem was replacing the foot pedal. I tried to improperly install the foot pedal spring several times. Once I figured out the proper spring installation all was well.
According to Thetford my two year old toilet shouldn't have had problems. Their assistance was to send an email with replacement seal kit numbers and a repair video.
Safe travels. JD