This serious vibration only occurs when in gear and parked, then disappears as soon as the car takes off. The engine does not really shake that much when I look at it under the hood and have someone engaging the transmission in Drive.
Would this problem still be due to engine mounts only (current mounts have about 100K Mi)?
It it was an ignition problem, it should happen all the time, right?
If it is only engine mounts, they are hydraulic and also available as less expensive after market parts: are these OK to use instead of MB parts?
THKS!

 

I would replace the engine mounts and maybe the transmission mount too. 100k miles is pretty good life from our mounts. I can not speak of the aftermarket mounts but from experience of aftermarket parts, I would avoid them. If you had a engine or ignition problem (i.e. misfire), you would see the engine shaking badly and have it at all speeds.

 

I just remembered that it does not vibrate when engaged in reverse or neutral at idle, but does vibrate when engage forward. Could it be the transmission, or does this mean than only one of the 2 engine mounts is bad and does not hold down the engine anymore when the torque from engaging forward is applied?...