I was looking for a brake caliper, the 4 pot version for the 16v due to a seized bleed nipple. I looked up the part number on the Realoem site and found that the same caliper is fitted to other BMWs. I ordered a R1100RS one second hand from German ebay for 12 euros.
When it arrived it was grubby but fully serviceable so I fitted new pistons and seals and fitted it to the bike. I was amazed at how easily it fitted into place with the 3 spoke wheel, I had never got them in that easily before. A closer look revealed that the hose and bleed nipple fittings were in a slightly different place to the original. As far as I can see the part numbers stamped on both the calipers are the same except for a "/1" on one of them.
It seems that the hose and bleed nipple holes are on each half of the original caliper and both on the outside half on the R1100RS caliper. This means that the banjo bolt is about 1 cm further outboard and allows the caliper to fit in and clear the rim much better.
If this is on any interest to others, then I will take pictures, let me know.