Itsy bitsy Head Gasket leak?

Hi there. I have a 1993 Grand Prix 3.1 with 370k on it. Now wait a moment. This car has been fanatically maintained from new by the original owner and looks and drives like it. Nothing has been spared. That said, the engine temp gague has started to rythmically fluctuate slightly and slowly at almost all times when warm (it has never overheated). Scanning the coolant temp sensor reveals a constant fluctuation between about 185 and 195 degrees. A new GM stat made no change. Also, I have noticed a very intermittent small coolant leak from around the upper rad hose at the rad tank whenever I've started it cold ( It is about -20 degrees here now). This small leak goes on untill the engine is half way warm and stops. A new rad hose and rad did not solve the problem. My question is: Am I looking at the beginnings of a small head gasket leak (not surprising given the milage)? I pressure tested the cooling system and the gague did not move a whit. I dont have alot of faith in the chemical block test products that are supposed to change colour in the presence of combustion gasses. These usually do "tell" unless the leak pretty obvious. My next step is to hook up a rad neck extension and put a little coolant in it to check for any rising bubbles while warming up. Or am I totally up the wrong tree on this? Stan