intake vs. head gasket leak

I have a 95 lumina with the 3.1 engine with a coolant leak. I have read many of the other posts on this site and am a bit confused. Last winter I would have to add a small amount of coolant regularly, about once a week. Then over the summer I never had to add anything at all. This winter it started again. I had a garage check it out and they said that they could not find any trace of an external leak so it was probably an internal head gasket leak. Now recently, twice it has left puddles of coolant on the ground. Looking at the front of the engine I can see evidence of the leakage. Some of the posts on here mention that the only way to know which gasket is leaking is to have a garage run some tests, others say that a head gasket never leaks external that it is always internal. There does not seem to be any oil in the radiator and there is no milky white look to the oil. Can someone help me figure out definitively which gasket is the culprit. Also, I have sort of intermediate experience at repairs, though pretty much a novice on this new a car, is this something that an average person can manage to change, or is it better to have it done. My Haynes manual makes it seem like a very complicated job. Thanks for any help anyone can give.

The temp induced leak makes it sound like a seal issue, with lower temps the rubber contracts and may not seal completely. At higher temps, the rubber is softer and more able to conform, and the metal sealing surface will also be expanded somewhat more and aid in sealing.

Around the front, huh? I have seen water pumps behave just like you described when the seal begins to go bad on them. Easiest way to check this would be to stuff a paper towel up behind the WP pulley and let it sit overnight. If it is cold-leaking, you should have some on the towel in the morning.

Also, cold water leaks at hose clamps are notorius for creating mystery coolant losses. Again, temperature plays a role. If the motor is anything other than stone cold, it may not leak. Just driving it into the shop to pressure test it may be enough warmth to stop the leak.

You might be getting the dreaded lower intake gasket syndrome, in which case it is fortunate that it is leaking out of, rather than into, the motor. If you look down behind the P/S pump, you can see the front seal and the seam between the heads and manifold pretty well. Check for tell-tale streaks of white residue coming from the seams if no wet coolant is noticed.