I was changing my oil yesterday, and while I was underneath my car I noticed some weird little gaps along the seam where the engine block and transmission meet. They looked dark inside, as if they opened right into the gearbox. And there were little rubber inserts inside them, which were very loosely placed. Anybody seen these before?? And what the heck are they?

I'll post a pic of what I'm talking about soon, I just didn't have time today.