My 92 735 168,000 miles lost a fan belt over heated for short time . Three weeks later developed antifreeze leak from head gasket just above engine block plug. I put in some raditor sealant. The leak stoped for short time and now I get intermittant white exhaust smoke. I suspect is leaking into the engine. What should I do? ignore? replace head gasket and do valve job, or get a new engine? My wife wants a new car? Any sugesstions? Is a head gasket hard to replace? Thank you