I refurbished a used BM57 after my original BM57 didn't allow shimming of the internal proportioning valve.

Problem is, on re-assembling and bench bleeding, I'm getting a dribble of fluid out of the port in the middle. I assume this is a tell-tale to let you know if the internal seals are passing.

20210207_154630 by DaveyBoyDave, on Flickr

Thing is, I just fitted new seals from a Bigg Redd refurb kit, so I'm confident they're good. There was some very light scoring/scuffing in the internal bore, which I dressed very slightly with fine sandpaper, but nothing that rang any alarm bells.

Any thoughts - or is the BMC just a duffer?