I have been a bit slack in regard to publishing my incoming mail. RailCorp sent me this nice letter over two weeks ago, and they appear to have relented and common sense has finally made an appearance. I now have a contact at RailCorp to call next time the bridge in question needs cleaning.
I also stirred the pot a bit by contacting the MP for Balmain, Verity Firth. She's written to the Minister for Transport about this bridge on my behalf, so hopefully that will give me a bit more leverage when I ask for the next coat of paint.