Just wondering if anyone has used a Filtermag at all. They attach to the body of your regular oil filter (tin can style) and are supposed to create a strong magnetic field to hold metal (ferrous) particles suspended in the oil to the wall of the oil filter. Given that BMWs (that I know of) use a plastic enclosure with a discreet internal filter, I'd assume that it will still work, but the magnetic field probably wouldn't be as dispersed as on a tin filter, i.e. if it actually works, and the particles would be stuck to the plastic enclosure rather than the filter cannister. Not a big issue given you simply would remove the magnet from the cover and wipe any trapped crap away before reapplying the magnet.
They also have flat magnets to attach to the outside face of your transmission. FilterMAG: Magnetic Oil Filters finish the Job Your Filter Started.