I don't think that the punkin needs a gasket or sealer. There is a seal where the driveshaft goes into the cup. Is the Boot over the universal not on correctly? That is the spot water can come in easiest. I think the swingarm has a drain hole in the bottom, can't remember for sure. But the answer to your question is ,no, no sealer required
Your punkin has holes in the pinion cup area to allow lube to vent into the cup. So yes, lube will drain out of those holes into the cup area. Make sure those holes are clear, aand put a slight bit of moly grease on the gear surfaces befor reinstaling. Have you pulled the driveshaft out of the cup yet? The seal should pop out with the driveshaft. Make sure that seal is reinstalled correctly. There are quite a few threads about rear maintance on the tech board. Remember search is your friend. There will be pictures and explanations on how to do the whole procedure
