I'm happy to read something looks good!
When I reassembled on the weekend, I was careful to get the secondary rotated well - could it be too tight?
The only change I made was I reduced the primary mirror tendency for lateral movement by slipping some plastic shims (approx 0.5mm thick from packaging) between the cork pads and the sides of the mirror. Not tightly, and in fact the mirror could still move (just), just not clunking from side to side when rotated.....