What kind of vibration are you talking about?
Are you sure it is not engine vibration?
I replaced my 16 year old transmission mount and I cannot say I felt much of a difference, if any, however they are quite cheap and I hear a good idea to replace

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Smoke Silver 1994 E220 Coupe Automatic
0 kilometers 6 September 1994
100,635 kilometers - 6 September 2010