I was looking at the passenger side motor mount on my 88 300E and noticed that under the mount on the top of the frame crossmember there is a big "splashing spill mark" of some liquid. It is dried out but I was wondering if these motor mounts are liquid filled and the liquid has been leaked out or maybe it is something totally irrelevant to the motor mounts (maybe some WD 40 that the previous owner spilled). The engine does not have any abnormal vibrations or anything except lately when I start the car at the moment it catches on I feel and hear a momentary brief "thump". Everything else seems fine. Any suggestions?