I've had the hole in the bowl gasket close up when the screws holding the bowl get tightened. Check the die cut hole in the gasket. Teflon coated ones tend to do it less, the black thick paper ones or brown ones are usually the culprit. Old bowl gaskets used to only punch one hole for the pump passage and if you put the gasket on backwards it would block the hole. Most new gaskets have two holes in them to prevent this problem.