tank on the radiator is leaking tranny fluid into the engine coolant. It can go one way sometimes or both ways a lot of the time.
DO NOT KEEP DRIVING IT!
It will destroy your transmission if you do.
Replace the radiator if you want to.
I recommend a after market cooler myself.
This happened to my sisters car, '98 Regal, and all she said was it was shifting funny, next oil change my dad found the good news, same as you here. Radiator leaked, and wiped out the tranny. Replaced the tranny with a used one he bought on line and drove up to Nebraska to get it. After all the work, time, and money, he said screw it, and asked me what I used for my cooler, and he installed one the exact same way on her car, totally bypassing the stock tranny cooler.
Not a leak, or a problem since for her.
I have been running a cooler on my GTP since 2001, and I dropped 40-45*F in operating temperature. I run a B&M supercooler I bought from Summit Racing. I use stainless steel braided fuel line, and some 1/4" male to male brass barbed fittings I bought from the local hard wear store. Where the lines come out of the transmission, and go from steel to rubber, i cut the rubber, and spliced in there for my cooler.
That's what I would suggest, not worth trusting GM's coolers IMO.
~F~
