1998 Buick Regal cracked head gasket?

I have had problems with my cooling system over the past 2 years or so. I had a very corroded radiator core that was filled with a rust colored debris and finally required replacement of the radiator about 5 months ago. Since the replacement the car has driven well and caused no problems. It did get very hot a few times a year ago before flushing the radiator and having it finally repaired (the radiator replacement). Then all of the sudden a few days ago it again got very hot after approximately 20 minutes of city driving. I took it to the mechanic and he said there was coolant leaking into the exhaust system or vice-versa, but he said this meant the head gasket was cracked and he recommended looking for a new car. He did not charge me for this bad news, but then I began to wonder is it really "curtains" for my trusty old Buick or should I fix the head gasket. Would commercial stop leak work? The car doesn't misfire at all as far as I can tell, but it does have a slight delay when you first throttle it on occasion.

Thanks,
Chris