I have discovered a brownish/yellow slime or oil in the coolant overflow resevour in my 1992 190E 2.6. It would appear to be oil leaking through from somewhere, however there's no sing of coolant in the oil, either on the dip stick or when drained for changing. Also, it appears that I have an oil leak around the head gasket.

Do these two seem related or could there be another cause for the coolant slime??