The seals and the little tophat spacers (brim of the "hat" is supposed to go inside the seal, though some put them in reversed for whatever reason) are all inexpensive maintenance items that your dealer should have. If you don't have a good local dealer, order from MAX BMW. I find it is good to bring in the top hat spacers as sometimes what shows up on the order list isn't the exact same width as what was on there/what it should be..
IDeally, one is supposed to remove, clean, inspect, regrease and replace the seals and spacers on the rear wheel every few years.