1992 Mercedes 300E engine shaking on P or N

[LexBenz]

Hi guys, I have this nice 1992 300E that I acquired about one and a half months and I already put 1,500 miles on it. I just noticed it last night when I came home from the shop after engine mounts replacement (Corteco) that when I put my car to Neutral or Park, the engine shakes continuously. My transmission mount is still okay (almost new according to the mechanic) so it was not replaced. But when I put the car in gear (D or R), it's very smooth. The previous owner claimed he replaced he spark plugs and wires. Any similar experience? Please advise. Thank you.