A bad head gasket will contaminate the coolant with oil.
There's alot of new/old products coolant additives, that clam to fix head gaskets.
The additives alone could contaminate the coolant system, we like to use metallic block seal for minor coolant leaks for this reason.I haven't used
www.steelseal.com yet!
Found a video
www.youtube.com/watch?v=3suQy44G_B0
Red Neck fix !
www.youtube.com/watch?v=7BjuAHBxnEw