I'm thinking about buying a 96 Mustang GT. The car is getting oil in the antifreeze. Has anyone else had this problem and what was causing the problem?

Im not an engine expert but i would stay far away from that car. I would actually avoid a 1996-1998 GT all together. I had a 1996 GT Before my WS-6, they have very restrictive heads from the factory and make 215 hp to the crank. If you like that body style look for a 1996-1998 Cobra that has the 32v 4.6, or a 1994-1995 GT with the 5.0. If you do end up buying the 1996 GT be ready to put new heads, cams and a manifold on it to make it any of decent (thats what i had to do).

The upper intake manifold is plastic on those years and have ALOT of problems. I wouldnt' doubt it if that is part of the issue.

sounds like a blown head gaskit