i have a 99 pontiac bonneville non supercharged. over the winter i had to change the radiator, ever since then the lower cooler line for the transmission going into the radiator has been leaking. not just leaking a consistent drip, its not coming from the threads but from behind the nut. no matter how much i tighten it it will not stop, i even took the radiator out and re installed the whole thing and it didnt help. could it be that the fitting needs to be re flared or what.

you mean the fitting is spinning in the rad? probably the fitting in the plastic is either stripped or there is a retainer in the tank thats turning or something. if you dont want to buy a new rad you could put an aftermarket trans cooler in it and dont go into the rad

It sounds like the flare on the line is damaged or the flange the flare goes against in the radiator is damaged. Or both are bad.

Ben 10 Alien Force! Bring it by Deano'* sometime and we can take a look at. We are certified Bonneville geniuses now!