2008 Cadillac Seville Radiator leak

If the radiator is leaking, replace the radiator.

If it's the common style with a crimped metal band around the tanks, you can ask at a radiator repair shop if they can recrimp it, but it will still have to be removed. Given the amount of work involved on GM cars to do this, I'd stick a new one in with a warranty.

As a point of interest, many leaks are caused by corrosion when the corrosion inhibitor additives in antifreeze wear out in about two years. Acids form in the system due to normal seepage of combustion gases. The red Dex-Cool, (Dex-Mud) antifreeze used by GM is especially prone to causing problems. Some mechanics don't mind it. Most want to get that stuff out and replace it with conventional antifreeze. Your independent mechanic will be able to offer advice on keeping the cooling system clean. He can test it for acid buildup too with a digital voltmeter.

If you're going to have a mechanic look at it; find a shop that can pressure test your cooling system. This test will help the mechanic find the leak BEFORE removing any parts. This way he is sure of what the problem is and can give you a more definite price quote for the repairs. Plus, you'll be assured that the problem will be fixed the first time.

By the way those metal pipes you mentioned are transmission fluid cooler lines. There is a small tank inside of the radiator (called a transmission cooler) which holds transmission fluid and cools it to prevent it from overheating the sends it back to the transmission.