most of the hard part have shiny finish to it ! but be carefull not all of them ! the best bet is to go with a knife and feel them as mentionned !
if you guys want to use losi pistons you need to off road ones ! you can also achieve the same by using black piston and drill them to either 56-57 or whateved size you want or 1,1,1.5 like we have been running.
As for the gear diff, the best one right now is the yokomo diff made by yokomo. It is the smoothest.