Successfully replaced my front brake disks yesterday. At 30K miles I was informed by a BMW tech that I had bad pulsing in my front brakes, caused by the disks, worn or warped.
I could feel the pulsing but had ignored it for a long time.
BMW gets $402 per disk plus hardware, plus an hour or two of labor. With the prospect of spending $1,000 for new disks (on a bike worth maybe $4500), I looked around for alternatives.
Beemerboneyard offer two disks for $469 including hardware
On Ebay, I found: https://www.ebay.com/itm/Front-Left-...53.m2749.l2649
for $210 for two, with delivery from UK supplier. The ad copy on ebay says OEM quality. No country of origin is listed. The box I received says motodisk brake rotors #239602, Japanese Standard SUS 420 Stainless Steel, Precision CNC MAchined, laser cut. They look identical to the ones that were on the bike since new. The new disks are rivet hardware style, not rotor hardware style. This relates to the manner in which the floating disk is secured to the wheel hub, and the way they prevent the disk from rattling.
The BMW K12GT documentation spells out the steps to install: Remove front fender, calipers and wheel, heat screws and remove disks, replace disks, tighten screws, try not to mess up the ABS ring, install new brake pads (from beemerboneyard $79.95), install front fender, check rotation of wheel clears ABS ring, Squeeze front brake lever to push out pads. Test ride. Smile.
Total investment: Approximately $300. Time Required: A few hours, as I was out on the road and walking back and forth to the apartment, etc.
I did the install on the street in front of my apartment. Used a small jack and piece of wood to jack up the bike at the headers underneath to lift the front wheel 1 inch. Took the unmounted wheel into the apartment and used a MAP/Propane torch to heat the screws to melt the thread locker. Cleaned and reused the screws. Used a torque wrench and everything. The heads of the screws look terrible (corrosion), so may replace them with new ones when I visit the dealer.
I did a gentle series of brake applications on my test ride to make sure all was working. I cannot feel any pulsing. I'll work up to some harder braking. Time will tell if the new disks will hold up and not warp.