ED80 Focuser problem

[step_hen]

Last night i noticed a problem with my celestron ED80 focuser. I have a skywatcher Autofocus fitted, and last night it refused to focus inward. I thought it might be the batteries but they checked out ok. Then i noticed that the drawtube itself was loose- I was able to rock it back and forth within the focuser. The problem with the inward focus was beacuse the weight of the diagonal and eyepiece were pulling the tube down in such a way that it 'caught' going in, but would be ok in the opposite direction. I played about with the two grub screws on the focuser but this didnt solve the problem. If i tightened them up the wobbling would stop but the grip on the tube would be too tight for movement. Has any one else experienced this problem or know how to solve it?