Well chaps,

Progress has been made ! I took off the machine bed and unscrewed the block with the lead nut in it. The Y axis moved easily and smoothly. BUT when I unscrewed the lead nut block it was 1.2 mm above the mounting on the gantry, so it was bowing the lead screw. I have shimmed the block and now it runs smoothly. I just need to finish reassembling and test it again.

Hopefully, End of Story.