First off, you need to check you oil more often than every 2500 miles. I recommend that you check at every fill-up or two. Engage the latch on the pump handle and pop the hood. That's with any vehicle, not just a Z.
If you are talking about the oil pan gasket, you probably got screwed. Gaskets that are under almost no pressure seldom fail. When the engine is running, oil gets sprayed around so that the gasket won't dry out (not that modern gaskets can dry out). And oil gets sloshed around when you accelerate and make turns.
If you are talking about the oil galley gasket, that another story. If you ran very low on oil, you may have damaged the engine.
If you use high-quality oil and filter (MANY threads on this site about which to use), no additives are needed.
Edit: You may want to run a Used Oil Analysis (UOA). That should tell you if you did any damage. Search is your friend.