I've never had one apart that's had any form of gasket or sealing agent on it. I bet they took the thermo out completely on yours... hence no oring so it would leak, thus using sealer to try and prevent it. I had to bypass the stat on one of mine once, I had to cut the centre of the stat out leaving just the outer ring and oring. It would not seal without the oring understandably. If you have it apart and in your hand you can see the oring will seal it.