Mine also had some play after 3000 km
Placed the tube rubber in the slots and it feels better, it even goes into 1 st gear much much smoother
What an inprovement

Use glue...
 

Go to a racing bicycle dealer and buy a tube of tubular tyre cement ( used to stick racing tyres on rims and very, very sticky...). Continental is probably best.

I carried out this mod using m/c inner tubes, each piece cut to wrap around a vane of the sprocket carrier ie. fit between adjacent cush drive blocks. Apply cement to the surfaces between blocks and pieces of inner tube. Fit the carrier using the vanes to push the tube pieces between the blocks with the cement acting as a lube. It won't be for long; once dry (24hrs) it keeps everything properly in place.