Im looking at a 450slc 1980 car is in great shape, but when started the engine makes a loud ticking or metel sound under the left bank valve cover. the owner says it is a exhust leak, but I have worked on more then enough engines to think it may be more. I just dont have any experiance with this engine, it starts fine and has great oil pressure, seems to idle a bit rough. it does not smoke, and the oil level is full. The odometer is showing 104000 miles. any ideas on how to proceed.