Locking the rear diff:
I filled my rear diff with SHELL SRS 4000 multipurpose grease...
Its high quality. (and probably not intended for RC use)
But it works better than I expected...
It does not totally lock the diff, but rather gives it a kind of LSD.
and it shure made my drifting a lot better....
(now i just have to buy some real drift tyres, I'm all out of electric tape.....[:-])

BTW: I'm running a TT01 calsonic skyline XB-built