Make sure that there is no space in .position and also replace n with the true name of the slider. Easiest thing to do is delete the n, put your cursor where it used to be, and drag the pick-whip (swirl icon near expression textbox) to the name of the slider effect.
> cheers Scott - no joy with that though. I just get errors when pasting it into each of the stacked layer's position parameters. Tried replacing 'n' with a name but no good.