A couple of years ago I, too, had leaking through the port discharge, assuming I understand that to be the port to which is attached the waste hose? If so, a guy I was then using for technical problems explained to me an easier fix. Of course, then being new to the pool scene, and not being at all a technical person, I have no idea why it was easier, but it may lend some credence to your issue. By the way, I also have a Hayward multiport.

What he did was install--and I don't know the technical name for it--a handle and ball assembly on that discharge port just a few inches from the multiport (before the waste hose attaches) which, when closed, stops the leak. When I need to backwash or waste, I then turn the handle and the assembly opens and I can do what I need to do, and then I close it again.

Elsie