I did the job by jacking up the car from the front driver side high enough to not lose much oil. Unfortunately I thought the o-ring was a simple 40mm o-ring so the one I had did not fit and the old one broke in half when I removed. However, I did my rear brakes and caliper repair about 2 years ago and ironically after I saw what the o-ring looked like once I removed it, I remembered the caliper repair kit having these 4 round rubber stoppers to protect the caliper.....the rubber stoppers were the exact size and thickness (not sure on thickness since old o-ring was brittle and flat) as the o-ring! Put that on and it was a perfect fit! Sealed everything up and was good to go. 10-15 minutes tops. And didn't lose much oil at all.

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1990 190E 3.0L