Why is there oil in my radiator? 1996 buick park avenue

A little bit could be OK. If it's a lot of oil, take it to a repair shop for a engine compression and a coolant system test.

I agree with tenspeed. A couple possible causes of this are a blown cylinder head gasket or a crack in the cyinder head.

Its not an overhead cam so the only place oil would be pressurised near coolant is either in the radiator or the engine block itself. A head gasket or head being cracked would be coolant in the oil.

If a pressure test is done on the cooling system then the oil cooler lines need to be removed from the radiator to prevent oil contamination.