How much oil is in the coolant - are you checking or seeing the coolant in the overflow tank?

Also has anyone ever use Redline WaterWetter in the coolant system of your car?

I ask because I have a 1998 C-230, For a number of years I had used WaterWetter. I noticed what seemed to be oil droplets in the coolant of the overflow tank and what looked like oil scum sticking on the sides of the overflow tank.

I MB tech told me a few drops of oil isn't a real issue, when the coolant starts to look like chocolate milk the issue is major.

After reading in these forums that WaterWetter may form a scum in the coolant I stopped using the Redline. Now at 97K miles and coolant changes every two or three years my overflow tank looks fine.