I've been thinking and tinkering more.  I basically held my finger behind the ball and it worked flawlessly.  I suspect the correct wireform for the ballgate is perhaps stopping the ball rolling backwards?

The part number in the manual is A-20604 which is what I had x 2 which is doesn't really work properly (as described prev post).  However Nicks is completely different and if its original for the BH then I reckon that would be my issue.  The only problem is that in the parts manual it has a disclaimer for A-20604 that (Part No. may vary with game).  In the BH manual I can't seem to find what the correct one is.