Use original seal
make SURE that the chamber is straight, and fits perfectly in-line to the engine - otherwise get it straightened/aligned perfectly by a good denter
DO NOT USE silicone, I have replaced many seals and used brand new engine oil, just coat the seal lightly with your fingers with new oil on both sides and fit. Someone may dis-agree with me here, but I haven't run into any problems with my method. If you have a better solution please let us know
since the engine will be lifted out, pulley bearings / seals, timing belt and associated parts, water body, engine mounts and of course cleaning of the engine bay