Aftermarket parts are ok replacements most of the time but motor mounts seem to be an exception.
I have a 92 300D and had to change out the original mounts at 130k miles. The mounts I used were aftermarket (febi). Even after I changed them, I still had some rattling in the engine compartment which I attributed to something else.
At 160,000 miles the motor started shaking again. This time I ordered Mercedes original mounts because the first ones had held up much better than the replacements. (130k vs 30k miles) The original mounts looked different in that they have a smooth hemispherical top as opposed to the fluted top on the replacements.
The car is smooth and the rattle is gone.
I suggest that you shop around because the original ones were only about 20% more in my case.

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