Pontic Aztek

I just bought a 02 Pontiac Aztek and I love the car, but unfortunately the person I bought it from was pretty dishonest. A couple weeks after I bought the car I noticed it was running hot while traveling up the mountain to go to work. I brought it to my mechanic and he had the hardest time trying to find the problem. Eventually, he had to replace the instrument cluster because the fans were not turning on bc of some electrical issue. He told me that the radiator had a small leak, but the people I bought it from put stop leak through it, so I shouldn’t worry about that. He said he wasn’t sure that the high speed fans were working because of an electrical issue with the BCM, but that he couldn’t do it because it was part of the theft system. I brought it to a dealer to get it fixed and they’re saying the high speed fan is running, but I need a new radiator. Help! Who should I listen too?!