The Losi XXX fits it's made of hard nylon so less chance of melting, you will need to ream a little out of the centre to fit the metric bearing though.
Part number A3079.
I strpped mine a couple of weeks ago as my slipper was too tight.
The RB5 idler is slightly smaller than the Rat / monkey one but the diff looks the same, not mic'd it up yet though.
I hope this helps.
