What does oil in the coolant LOOK like?

[Strider]

I recently had the hose from the head to the heater split on my 91 300E. In looking at the inside of my coolant expansion tank, I am finding gunky deposits that are light brown / tan to white in color, and thick like grease, not oil such as you'd find in dirty dishwater. I was thinking that I didn't rinse all of the flushing agent out last time, which was pretty foamy. It feels kind of like soapy scum, but that could be wishful thinking on my part, slick is slick.

I'm not finding anything wrong with the motor oil, and I can't see where the level has dropped since I changed it last.

Please?

Thanks,