I had that happen to me once. When i noticed it it was too late, the timing belt pulley on the crank was so wallowed out that it walked into the crank seal on the oil pump, and started spewing oil every where. The worst part was, i was a hundred miles from home.
Fixed it with a new timing belt pulley, keyway, crank seal, and new timing cover because the main crank pulley ate up the cover.