Depends on where it is originating from. Helicoils do not seal themselves, so unless the gasket/washer is sealing on the cases outside of the diameter of the outer helicoil threads, that won't help.
Check to see if the helicoil is protruding slightly past the face of the washer/gasket surface as well.
Maybe there's some leakage in the JBweld to case area?
Is the gasket surface on the case perfectly flat and perpendicular to the bolt cenerline?
How about a picture?
I've switched all my bikes to a Zip-Ty drain plug. It's aluminum, so the risk of damaging the case threads is greatly reduced. Plus the bright blue anodizing provides a nice farkle factor. With a skid plate to protect the bottom, it's all good.