Actionscript 3 :: Infinite Horizontal Scroll At Constant Speed Using TweenLite?

I need to do an endless horizontal scroll of elements within a parent MovieClip.No matter what ever method I try, an element of 'drift' occurs and eventually the elements start to overlap.I've tried using relative recursive tweening for each element according but this method seems prone to quite a bit of error after repeated starts and stops.

//CODE START
function doScroll():void {
TweenLite.to(this, .25, {x:"20", ease:Linear.easeNone,onUpdate:checkPos,onComplete:doScroll});
}
//CODE END

I've reverted to doing absolute tweens to a predefined position using a contant speed. This seems to be more accurate but still some 'drift' occurs.

//CODE START
//_dest is predefined
var speed:Number = 500;
var dist:Number = this.x - _dest;

[code]....