i have a 2003 c240, i was looking in the trunk and i look up to the deck where the speaker is, the are 3 nuts that look like they attach the back deck to the the frame about 2 inches in from the trunk opening. 1 is on the left and one in the middle and one on the right, well the one on the right side has oil on it, i put my finger on it to see what it was, its oil, i wonder if its from the motor that pushes up the rear screen, can anyone help?

 

The early C's had the rear sunscreen mechanism lubricated with too much grease and of the wrong type so it gummed up and failed. Sounds like yours was cleaned and overly lubricated with the wrong grease/oil again. Just guessing.

 

I think it is a good guess. There is nowhere else it could possibly come from.