intake vs. head gasket leak

[paulski617]

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.