Working on a 1993 940 non turbo. Started out changing the water pump due to leakage in of the gasket. Noticed when installing the new anti freeze that the was a fair amount of air bubbles coming up in the over fill tank. Thought is was just air getting out of system. Filled to max level.
Problem is that is appears that I am getting excessive pressure in the tank. Looks like it is leaking at the seams, but only after running hard. With the "air" and the leak after running hard, is this looking like a head gasket problem?
Car runs great, no smoke but I thinking it could be a break letting pressure into the water jacket. If this is the case, has anyone used Moroso Ceramic Seal to fix the problem. I know if a head gasket is broken it should replaced, but I am trying the "easy" way out. Also the car is running at normal operating temperature, with no fast warm up or the needle going over the center mark.
Any input would be appreciated.

Neal