After valve covers, what is the most common place for GS 400 V8 engines to leak oil onto the exhaust and ground?

 

Welcome to CL. I see you are a brand-new poster.

Oil on the ground, of course, can come from a number of sources.....oil-pan gasket, drain-plug worn or not tightened enough (you should generally use a new washer for the drain-plug at each oil change), bad oil-filter O-ring, damaged filter, filter not tightened enough, cracked or worn engine main-seals, or a leaking oil-pump. Oil on the exhaust-pipes, as you note, is most likely to come from either the valve-cover gaskets/seals or the valve-covers/cylinder heads themselves getting warped from overheating. With small leaks, If the engine is worn from high-mileage, sometimes the use of special high-mileage ois, which has a thick viscosity that is more resistant to small leaks, will cure the problem temporarily.....but major-repair or engine rebuilds can't be put off forever. And, of course, on a cold-start, the thicker oil will make the starter work harder to crank in very cold weather.