I looked an 87 GTS for sale and the coolant recovery tank / overflow was filled with black, yes, black sludge. So I popped the radiator cap and to my surprise, it was a relatively clear green with only a little bit that multi-colored trace of oil in it. I usually suspect oil in the coolant to mean head gasket issues, am I off the mark here or not?
When you leave very old fluid in the resivour, it will turn really dark a molded- thats normal but clean it all up and you should be good- I f you had any kind of leaks you would be smoking badly...
Hmmm, this stuff wasn't dark brown, it was black sludge, like an oil slick. Didn't notice any white smoke or sweet smell either. Weird...
When I bought my Celi, the overflow tank was like that too. Just wash it out, flush the rad. and you should be golden! edit: also, check your spark plugs for coolant residue. If theres coolant on them, it's a bigger problem. I don't know exactly what it is or how to fix it though, ask Mafix
