We have the Thetford Aqua-magic Style II. The seal is not leaking - yet, (still holds water in the bowl) but it has slid to one side. After donning the "rubber glove" I attempted to re-center it but it wouldn't budge. I downloaded the manual from Thetford and it appears you have to remove the toliet and disassemble it to replace the seal. So, I guess the "if it ain't broke don't fix it" rule will apply for awhile.