Q: Repeated oil leaks

I noticed an odor in my car cabin a while ago, but didn't see any fluids or oil on the garage floor. When I got it looked at, the dealership found a bit of oil dripping on the exhaust manifold, which had been producing a little smoke and the odor. They replaced a gasket, and the problem was fixed. Recently, I started smelling odors again. This time, I see oil on the garage floor. Not a whole lot, but I was under the impression expensive cars should leak at all. I'm taking it back in to get it looked at, but is it common for gaskets to go bad? What other common things might happen that would cause my beamer to leak oil?