I’ve been a little concerned about the play in my RA axis since taking it apart and have just found this article which seems to give me the solution: http://timsastroblog.blogspot.com/2007/04/little-tune-up-for-eq6.html

It seems I would have got there in the end as I’d narrowed the error down to adjustments of the worm screws but it’s nice to see the problem documented this way, well done Tim.