More info that might be useful to other 6040 owners.

Investigating the play in the crosswise bearings I thought I spotted the support rails out of parallel, quick check with builders level confirmed it. I loosened off the holding screws, got some mulgrips on there and twisted the top one, couldn't feel any movement at either end. About to give up but tried the lower rail, twist... what was that? was that dirt or did the rail move, yup it looks like an eccentric end connection. Check with the level, now looks true. Do it up tight and yank on the spindle holder ...play in the crosswise bearings has gone.

Very pleased with myself as I didn't know they had eccentric ends.

So now all I can feel is flexibilty, and I can't complain about that because I knew the construction I was buying. And some bearing run-out which might get fixed by a new spindle.

I repeated a run that I did earlier. It was quieter, and got a better result. But still some problem, on tangent lead in and the tabs the tool goes inside the profile