Go to www.thetford-europe.com
click on 'Customer service'
click on 'User information' on the right side of the picture.
click on 'owner manuals and Installaton instructions' right side of picture.
click on top left picture 'Built in toilets'
click on c2/c3/c4 n 'installation instructions' bottom section to right of picture.
Click the open file in the download window.
wait for it to complete downloading then save it to your h/disc. Just revers the instructions for fitting.
hope it helps. My guess is you will have to replace it. But you could e-mail thetford on the 'ask thetford' what can be used to seal off a leak.
Bob
February 2009