I have a 300D 2.5 and changed the motor mounts with aftermarket mounts at 131k miles. I think they were Febis. They only lasted 30 k miles. Even when they were new I had some rattling noises which I thought were noisy lifters or something. I assumed that the noises could not be related to the mounts since they were new.
When they failed I decided to replace them with original parts.
The original mounts are higher quality and even look better than the aftermarket mounts. They come with a 12 month unlimited mileage warranty. When I installed them all of the noises went away.

Caliber Motors (800-252-6877) gives 20% discounts and their price was not much more than the other parts houses.
Phil at Fastlane can get original Mercedes parts for you if you ask him.

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Tom Hughes
St. Louis
84 300SD
92 300D
86 300SDL