seal replacement

i am ready to pull my hair out!!!!??? does anyone know where i can get replacement seals for my canvas? i have been looking for weeks and nothing i have come across is an exact match... Ameritex Fabric Systems Sure Seal was what i was hoping to grab (still don't think they will fit right) but...

Had to replace one of the toilet seals on our 400 Sedan Bridge during summer holidays last year. Figured I'd capture the glory of the event and share it with the world :-) Hope it sheds some light on this straightforward project and that it might help someone else. http://youtu.be/Qi5F1NqE5Is