Just a quick update for others who may encounter such a problem: I backed off the RA meshing a bit (as per AstroBaby's site) and the spikes seem to have gone. I think it was RA sticking, as before the adjustment I could hear a slight change in tone as it rotated when slowly slewing.
Of course, I have more backlash than a Trump tweet now!
But biasing the balance to the east seems to help with that.
Thanks all for the advice.
Other things like counterweight bar I may leave as I'm waiting on a new mount arriving anyway in the next couple of months
Thanks again.
Paul