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Petrolium based product; the O rings are impervious to just about everything. You can easily use motor oil, tranny fluid, no problem. They stand up to gasoline, they are pretty rugged little dudes. About the only thing I've ever seen cause a problem is brake fluid, tends to make them swell up a bit which pretty much defeats the purpose of lubing. Never had, or heard of, a problem with lithium grease. WD-40 on the other hand, evaporates- and according to the WD-40 bulk product safety sheet has a flashpoint of 120F and should be kept away from all heat, flame, and sources of ignition. I don't think using it on an engine would be wise.