I Have a W124 and it has cover plates not plugs. They keep dirt out and dont seem to collect moisture too badly. I have a very nice floor jack but some times i still use my factory jack points as they are very easy to get jack stands under when used with the factory jack. Mercedes jacks are so much nicer and more efficient than what ford/chevy/dodge provide.

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1991 300d 2.5 Turbo OM602