Well I've gone against George's good advice and shimmed the bearings to remove some of the end play.
Sorry George I do respect your advice and I know your right but I decided the bearings are worn anyway so if shimming them totally knackers them I've not lost too much!
So far since I've put it back together, there's no longer a clunking / knocking sound when changing direction and it's ran the same program that caused it to miss a load of steps without problems, so fingers crossed the bearings will last a bit longer and not collapse under the increased preload.
Thinking of buying a coarse diamond whetstone to stone the slide down a bit at the ends to remove a bit of the friction in the Y axis at the ends, will this work?
Thinking of these they should get into the dovetail too.
Forge-Steel-Diamond-Sharpening-Pad-6-x-2-3-Pc
Cheers
Chris