The crankshaft throws oil to that side of the engine. Since there is no baffle, oil is getting thrown right out that slot. I had the same thing happen to me years ago. As I recall, you can't just plug the slot due to the way it works. I have since found some dual action fuel pumps that were more vintage, and they don't appear to be set up like this one is. Perhaps you can hunt around and find a different version. Otherwise, switch to electric wipers. There work better anyway. The dual action pump I had on my '53 helped, but it was nothing like electric.
