We really need more info.
OEM parts or did you make things up.
OEM from were? another W108
New or old tranny and engine mounts?
Drive shaft. was it sortened? Was it rebalanced if cut?
when removing the drive shaft did you put it back in the same orientaiton that it came out in.
I know in the W123 there are marks to make sure the drive shaft is installed in the correct orientation or it will vibrate. did you insure this?
Pressure plate/clutch assembly OEM or rigged? could be out of alignment. Was it installed properly with an alignment shaft?

We need more info.
Give us details of the job and your abilities. Have you worked on mercedes before? or are you new to them?

Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car