2003 Rincon clutches and case questions

So tore down the engine because it stopped pulling when going up inclines, Found one of the o-rings was destroyed, Also noticed a 2mm crack in the center case behind the clutch. Anybody else run across this and if so is it a huge problem? Second question is I want to change the clutches while im in there, do i go back oem or anybody recommend and hi-pro ones?