Hi Mike,
It's over 20 years since I last built one of the Ratio signal kits and my memory is bad at the best of times
. In fact, I don't even remember the platform being made out of brass, I thought it was plastic although I suppose they could have changed the materials over the years.
I do remember the filaments that they provide as they tend to use them in a number of their other kits but I can't for the life of me remember what adhesive I have used on them. To me they always look like a nylon material and as a first choice I would probably have tried superglue although as you have already discovered that doesn't appear to work too well. I am surprised that the Revell Contacta does the trick because it normally requires both surfaces to be soluble in order to weld them together but who cares if it works?
When superglue and the plastic solvents have failed I have had some success with "Bison Plastic Adhesive" on hard plastics. It is available from Maplins.
As an alternative to using the filaments have you considered making your own posts and handrails? I have found that Peco N-gauge trackpins with the points cut off make reasonable posts. You can drill a 0.5mm hole through the platform and feed them through from the underside. A tiny drop of superglue on the head makes for a really strong fixing. For the handrails I use very fine fuse wire wrapping it around the posts and once again securing it with the tiniest drop of superglue. Just an idea if the dreaded filaments start to drive you round the bend
