How often i should service my balls diff...

[vrooom]

I race my buggy once a week. So how often i should service my buggy's ball diff?

My diff is really crunchy/gritty, so bad it makes me barf.

I use those hardened black/grey balls... but can you get hardened diff plates?

[HOTSHOT III]

Sounds like it needs a rebuild. Last time I did mine I followed this method:

http://www.rctech.net/forum/electric-off-road/512013-how-properly-build-break-ball-differential-slipper-clutch.html

The break-in process in particular made a huge improvement over my earlier attempts, it was a bit time-consuming but to date i've done the equivalent of 6 race meetings and they show no signs of deteriorating. Hope it helps.