I have sterted to make these repair kits for the front brake master cylinder on all 1100 bikes, except S. So it will fit all 1100 R and K, and R850R. the OEM part number is 32722332037.
What I sell are only the two seals, and not the piston. The piston is not an item that wears, the seals are. If the brake fluid was not changed as it should be, every 2 years or every 20.000 kms, it starts to crystallize and the seals rub agains the crystals, so that the brake system starts to leak. Not only is this dangerous (the front brake takes care of 70% of the motorcycle mass) but if dripping, it can ruin the nice paint on your fairing/tank.
The seals I make give you the nice ferm feeling of braking, like a set of steel reinforced brake lines. Don't imagine that it will be on/off, but you will definetly feel the lever more ferm.
The dealer price for such a kit is ~90$, my price is 39$, shipping included worldwide!
Don't wait until your cylinder starts dripping, change the seals now. It will definetly change the way you interact and feel with/ the bike. Changing them takes ~ 30 mins. No need to visit your repair shop for these. Just empty the top reservoir, put some rags on the tank/fairing, take off the brake lever, undo the screw that holds the piston inside the pump and be careful to it as it tends to jump. Once you got it out, change the seals, clean the inside of the pump using a clean toothbrush (that you are not going to use anymore) and install in reverse order of dismantling. Then pour in brake fluid from a sealed container and put a coin over the small hole/s in the reservoir. Squeze the lever a couple of times untin no air comes out and put the lid back on. That's it!