OP, if the pump sat for 3 years the gasket might have dried out enough it started to leak. Tightening it may have bought some time. You should consider getting a rebuild kit to keep on hand in case it starts leaking again.
I had a Surflo that was starting to drip at the same place. It was going to need the gasket replaced and you can't buy them separately. Instead of ordering a rebuild kit I needed a working pump immediately so I replaced it with a Surflo Revolution which is quieter. I saved the old pump to rebuild as a spare, but haven't done anything with it yet.