There appears to be oil in the coolant expansion tank on my '95 C280. (M104) There are semi-floating globular masses that feel sticky to the touch. Is there an easy and definative way to tell if it is engine oil or transmission oil? There dosen't appear to be much color to the globs so far, so I can't use that to help find out. The head gasket was replaced at 32,000 miles, and the car now has 97,000. The coolant was changed recently (3,000 miles). Could the coolant take on these characteristics without oil seeping in? The car runs fine, uses no oil and has no cooling problems.