When it comes to hydraulic masters, the RCS series by Brembo racing is the absolute best there is. This brake master will be a perfect fit for your BMW K- or R-series build and will work with both the original brake calipers and big 4-piston calipers like used on the S1000RR.

The 17RCS by Brembo Racing comes without a reservoir, so for true plug&play make sure to add the Brembo RCS brake reservoir. 

Comes including banjo bolt, lever, integrated brake switch, and takes DOT4 or DOT5.1 brake fluid.