I have been finding this stuff lately on the 394 in my 63, a wet green slime type material the consistency of snot, and its been gumming up in the pcv and the filler tube/breather cap pretty good. I know these types of issues usually means somethings terribly wrong with the fluids in the car, however there may be an explanation. I had changed the thermostat/housing gasket and made a slight mess of things due to not being able to properly drain the fluid first short of a siphon hose (which I later did the second time since it leaked and still weeps). maybe some of this coolant leaked into the manifold/crankcase area? are there other causes for this green stuff? the car doesn't run hot at all even on long rides although its wintertime now, and the fluid in the rad seems to be fine other than the slight weep from the housing gasket still when it sits. I took pics of underneath the valve cover on the driver side last summer and they seemed not too bad then, although ive driven it a lot since then. it does drip oil slightly, and strangely it the level hasn't been going down (which hopefully doesn't mean excess fluid coming in), but I did add a bars oil stop leak concentrate to slow this down but it still does very slightly so its very hard to tell. I know leakdown tests help to find leaks in the head gasket and such but idk if its even a coolant leak problem. I just hope I haven't done any serious damage driving the car this way, as it seems to be running pretty dang good. is the green stuff def evaporated coolant or ate there other things to look for? change the oil asap right? all advice is helpful!