From experience......
We had a 97' Ford Escort, bought it from my best friends dad, he hit a deer with it. My dad is rather auto body saavy so we fixed it up and drove it. It always seemed to run hot (not over heating) but... hotter than youd link a little 4 banger would... Head Gasket ended up going out after about 20,000 miles put on it since we owned it. We had it fixed. when the head was apart. There was a goo all over inside the water jackets. I talked to my friend. the radiator had been leeking off and on. They kept putting the Bar no leak stuff in there.. (comes in a black bottle and sounds like water with chunks of crap in it..) well.. in a nut shell. we pulled the radiator. could see crap in there..... replaced the head gasket and radiator.. thing never ran better and cool as freakin ice.. (not quite....)
just my 2 cents... the stop leak stuff is a band-aide. I'd suggest... ESPECIALLY if you're going to race it.. you have it fixed proper.