Martin W…
I reckon you're on to something there…
'Tell me from the pictures posted by George on this thread and the replacement dial there are far more marks on the dial face is that important or just more chances at starting?'
Martin B … Judging by the TPI chart numbered 1 – 6, I make the assumption that you should be able to pick up threading on any number diametrically opposite ea. other to get the same TPI ,instead of waiting for the dial to come round again…

i.e. … 1 – 7, 2 – 8, 3 – 9, 4 – 10 etc.

Not having done any single point…yet … always used the tailstock die holder for the small amounts I've done; so I am making the assumption…

As an after thought… check the positioning of your leadscrew centre, may be the design has been altered…
I might have sussed it, took some more measurements…take into account camera parallax error… your hole centre looks approx 11 – 12mm from the edge of your saddle… mine is 6 – 7 mm from the edge of my saddle, a difference of 5 -6 mm… voila! your radius of arc is greater than mine hence your gear will swing further round than mine hence contacting on the bottom of the gear not on centre line… if you get my drift, …solution … plug the original hole & redrill approx' 6mm closer to the edge of your saddle. I know you've already resolved it so to speak with the spacer but…
George.