I know this is a late reply, but if you are still using your 808 and continue to have problems, I eliminated this problem once and for all on the 808 (2008-2010) here:
viewtopic.php?f=9&t=12537The official solution (adding another bearing) sucked as much as the original design, the only proper fix is to use a pinion with a smaller (conventional) shaft so that a much more durable bearing with larger balls can be used.
They obviously rectified this from 2011-onwards by going back to the conventional design, but the 808 was a strong car apart from this problem. Mine's still going on the same diffs, 5S brushless converted.