I'm trying to order a pair of rear brake discs from germanautoparts.com, and in order to get the right one, they ask for the PR code (either ON5 or ON6). Supposedly, it's on the sticker attached to the front cover of my maintainance booklet. I found the code for the front brake discs (1LF) but I can't find the other code anywhere. Does anyone know how I might go about finding out which one it is?