if its the same as mine, its the transmission and power steering cooler just like the other guy said. its like a mini radiator to cool those fluids down. and your best bet is replacing the whole radiator. no point in doing a half ass job, just for the rest of the radiator to take a crap on you sometime in the near future. I just replaced the rad in my 05 and i dont have very much experience with working on cars, just started getting back into it and it only took me about an hour and 45 minutes tops to take it all apart and back together. and that was with bull****ting with a buddy of mine. thing that took the longest was draining coolant and getting it back to operating temp to test it out lol