I had a small leak on one of my bulkheads due to a crack from "possibly" over tightening. I had to buy a new generic bulkhead and replace the old one. Take off your bulkhead and examine it closely. You may want to check your gasket and/or replace it. Some folks use silicone to get a sealed fit, however I choose not to. If your bulkhead is the correct size and you have a new gasket, you should not have a leak.
It took me quite some time to fine the small crack in the bulkhead. I must have plumbed that sump five times before I figured out where the leak was coming from. I use barbed and threaded fittings, so I did not have to cut or replace any pipes so that helped my cause immensely.
Good luck!