Any suggestions for lubricating O-Rings that are used for water pumps,
basically I want to extend useful life as much as possible. Someone
suggested lithium grease?

SD

Petroleum Jelly (Vaseline)

I don't think so---will eventually ruin the O ring
mld

I do. Petroleum and Butyl rubber are completely compatible.
Use of Vaseline on Buna-n O-rings is a standard procedure.