There's only one way to find out--and that would be easier than changing the seal and gasket first---you'll still need to clear the passageway. Maybe a vacuum could suck out the blockage. I'd use an open safety pin--has something to hold onto while probing and thin enough blade not to knock the plug into the axle tube all in one shot.
If your car has a stamped steel cover on the pumpkin (they can and do rust through) I'd look to replace it with an aluminum one from a later car (which I have done) -- or buy a chromed one (for Jeeps-cheap) listed in JCWhitney (which I have not done). -- Dave