If you replaced the engine mounts, I don't see how that much vibration could be transmitted to the passenger compartment. Are you sure you used the correct ones - i.e. not those for the six?

Mine is a W102, and the first exhaust support is solidly bolted to the back of the transmission. The tranny mount supports very little weight - it is designed just to fix the location of that point, and provide vibration isolation - the mount is very soft. If it has hardened, exhaust vibration will couple in there.

I am more concerned that replacing the motor mounts did not substantially solve your problem.

Steve