The way I always fixed Slip-o-matics (Crayfords) is by removing the pinion shaft, removing the knobs and then shrinking a shrink tube onto the shaft. This puts tension on the drawtube and increases friction. 100% better and cheap as chips, no glue needed, no abrasion of components as you get with sandpaper.
$1 per foot...
http://www.readytoflyquads.com/3-0mm...ink-tube-black