I have not bought the hardened spacer what I have done is similar to the above post but works a treat for me. No extra parts needed either.
Both halves of the gearbox casing there is a recess for a bearing, one is used one is not, the empty side is for changing from mm to rear motor, 3 or 4 gear etc. what I have done is put a bearing in both sides of the gear box case, which means the lay shaft gear now runs up against a bearing rather than the spacer, and then cut down the spacer to suit the gap between the 2 bearings.
I didn't have calipers at the time to measure the size of the spacer I ended up with but there is now no wear on the spacer as it runs on 2 bearings and the layshaft also now runs on a bearing instead on up against the spacers causing friction and causing the spacer to wear.
The spacer needs to be cut exact otherwise when everything is tightened up the bearings may push out of the case slightly.
I have had trouble with with the slipper since the day I got the car (one of he first batch) and only since doing this have I got a slipper I can tighten and adjust properly and now is fantastic, run it for 6 months now with same AE pads and no slpping
