Sounds like the Buick needs to be properly diagnosed. I would pressure test the cooling system after replacing the radiator. Radiators on a L36 3800 are not hard to replace and are cheap as well, replace it first. Second pressure test it , you may find a leak anywhere from a hose to the plastic coolant elbows. If nothing visible is leaking on a pressure test well then block test it. Rule out a internal leak before you scrap it. GM 3800 are not known for head gasket problems, Ford essex 3.8 well thats another story. I owned a 97 GTP L67 , went to 280k before the 4t65E trans blew. I had a leaking rad , bad intake gaskets and leaking coolant elbows. Fixed those and never had a problem with the car for another 50K.