Hi there,
I agree with Neil about the Jenolite as preparation for painting.
However, are you sure you've totally got rid of all traces of the Nitromors? I think you rinse with white spirit but I'm not sure about that – I expect the instructions on the tin will tell you.
Personally, I'd have a go at the corrosion-stained patches with a fibreglass pencil followed by an abrasive filled rubber. Years ago, one brand was called a 'Rust-Rubber' but more recently I've seen them advertised by Garryson (usual disclaimer).
Best regards,
Swarf, Mostly!