Looks very nice Pete, nice round stars which is the toughest bit to get right.
how did you manage to get it horizontal? ideally, you loosen the opposite side a little then tighten the other side for each iteration, unless you loosened and the altitude was sticking and not reducing as you loosened.
when you have it dismounted, try removing both screws, and turn mount in altitude by hand a few times to see if it moves freely, looking at pics of the vixen sp mount, I can see an altitude adjustment only on one side, so not sure how it works.
anyways, have a play at drift alignment with phd ver 2.
its got a drift align wizard and lets you drift and adjust and watch trendlines.
very handy and can get you aligned in 15 minutes.
http://openphdguiding.org/
http://openphdguiding.org/man/Tools.htm#Drift_Align
same with pempro. not sure what you're using but I've spent many hours on alignment as well and wasted precious clear sky time.
Cheers
Alistair