Standard 3760/3761
Also, Viton has the widest range of resistance to chemicals. It’s resistant to several chemicals like silicone oil & grease, mineral & vegetable oil, aliphatic, chlorinated hydrocarbons, methanol fuels, and so many more.
Once you have selected the most suitable seal available, considering the environment, temperature, shaft speed, pressure, lubrication availability, as well as the size, of course, the seal should be stored adequately and then fitted properly. Here are a few suggestions that could help:-
Rubber type
Rotary Wheel Of Auto Parts
Place the ruler or straight-edge on edge diagonally across the head and block and look for gaps showing light anywhere between the ruler and block.

Put a wooden block or a piece of large tube against the seal and gently tap it squarely into the housing until it is fully home. Refit the timing cover, if removed.