I just had the same problem on my 95 LS. It was taken care of at the dealership, while I was having the timing belt and brake master cylinder replaced. Its a pretty minor job. The part is only like $10-$15 and there is almost no labor. The exhaust camshaft is behind your plug that's leaking. That's why oil sometimes leaks out from behind. Oil leaked on my car behind the headers just like on your car. Since the replacement several months ago, I've had no smell of oil and no visible leaks in the engine bay. This is also sometimes called a "cam plug or camshaft plug".