Oil leaks

I have a 2000 Bonneville and 2000 Grand Prix, both with 3.8L engines and both with about 100k miles. Both have small oil leaks somewhere on the engine which I can't readily find and which result in a burned oil smell. They don't leak much because I can find only an occasional drop of oil on the driveway. Is this a common problem and what is required to repair - parts required, cost, etc? I'm sure this is a common problem - I just don't know the exact cause. I've heard something about intake manifold. Thanks.