Generally speaking, most BMW enthusiasts prefer Redline fluids for the trans & diff. That's what I would recommend, or perhaps Royal Purple products, which is what I have in my car. You'll have to verify ahead of time which kind of fluid your transmission takes, since there was some variation in the required fluid over the years. There should be a sticker on the side of your transmission. For the diff, you will need to determine whether or not your 325 has a limited slip differential before making a fluid choice. You most likely don't have an LSD, unless your car is equipped with the cold weather package and no ASC. If you do have an LSD, you'll need to make sure you choose a fluid with the appropriate friction modifiers. The viscosity for the diff should be 75w90.
Last edited by ZeGerman; 10-02-2012 at 02:39 PM.