Ouch. I can picture it now and see why the force could cause some damage. Here's a schematic
that might help you fix it yourself.
I still think your best bet is to contact Thetford. Have you checked out the "Ask Thetford
" part of the website? Or you can go here for their Service Centers
It's a long shot, but I had a marine portable one on a sail boat that needed to be lubricated. Our cassette seal was jammed once from sitting unused for a year and I used silicon spray to loosen it - in case you haven't already tried that. Good luck.