Righto - a $14.00 fix from AutoPro for a 2x3 foot sheet of 2mm cork. I cut a ring of it out and fitted it just fine. It's slightly thicker than the old one, so it will either last longer (which is good)
or it will be too springy (which is bad).
Either way - it works just great.
So, the Dec side is all back together with about 90% mesh, which is as good as it gets without having to resort to twisting the motor/worm mount.
I put it all back together with new grease and it's lovely and smooth.
Now that I can lock Dec again, I'll invert the whole scope on its face and do the RA unit.