I saw your plug post with pics, they do look ready for a rebuild kit, but I wonder it that is really the issue. Both look similar while th issue is ont he port side only.
wonder, it could just be the pic but - is it possible there is a gap in the intake tunnel:
View attachment 174465
This being a negative pressure side of the pump/tunnel, if it really is a gap left after sealant fell out it could be where the pump sucks air from the bilge, it would explain the symptoms.
I used to use 5200 to reseal, but lately went with bondo (more work to hone it smooth but the effects are pretty good, and no gaps to leak air into the tunnel:
View attachment 174466
Just thinking out loud...