I have painted the heater blower now, not done a great job, but it’ll do, it’s far better than it was. At least now it’s build some pressure and move some more air. Reassembly is next, re-fix the resistor to the side of the housing and re-solder the wires to the fan motor.
I phoned Flag, who’s paint I used, to find out how it was going to do covering the Sika Flex brand sealant I had used to fill some of the gaps. The nice person I spoke with didn’t seem to understand the question very well, and given that the worse case seemed to be that the paint wont take to the polyurethane, I just went ahead and gave it a coat. Whats the worst that’ll happen?