I would say that if it were just a "film" or mist of oil inside that wouldn't be abnormal, but if there is enough such that it can collect into a visible "puddle" at the bottom of the can, that isn't so good. The O ring may appear superficially to be OK, but it may still be allowing some leakage, though if there is a problem it may not be at the O ring, but further back at the front of the crank. Some others have had more recent experience working in this area who will probably ring in shortly..