Keep an eye on the heater in the car. I have a 75 which had the same problem. It drove fine, no probs at all, but then the heater matrix became blocked with the emulsion so only put out cold air and then the engine started to run slightly hotter, especially when I came to a standstill.
Turned out the head gasket WAS away !!!
If you are getting oil in the coolant, I would say you definately have a problem. Check the expansion bottle, if it is starting to fill with emulsion then get it sorted soon.