My handbrake got "sticky" over time, meaning that the brake lever wouldn't get all the way back to its resting position upon release and I had to push it ever so slightly with the back of my fingers after each squeeze. 

Two separate BMW technicians diagnosed a weakened master cylinder that had to be replaced eventually. I had no other symptoms such as leaking, so I was a bit skeptical. On a hunch, I disassembled the handbrake using the diagram below and, lo and behold, I discovered that the lever mounting pin was all dry and rusty. I applied a touch of lithium grease to the pin and put the break assembly back together - voilà! problem solved.


Some notes of caution: The instructions above are for replacing the master cylinder; you should only perform the steps highlighted in yellow to remove, lubricate, and put back the mounting pin. Don't even think of adjusting the thrust pin attached to the brake lever (slotted flat screw head sealed with red paint) as I learned the hard way : it could cause the brake to lock up when the fluid heats up and expands. Finally, keep in mind that the mounting pin is tightly screwed in and secured with Tuflok. Make sure you use a METRIC, good-quality hex key (Allen wrench) of the right size (5 mm) because there is a a significant risk of rounding out the head as mentioned by "MT350Explorer" in this post:
https://www.k100-forum.com/t5082-changing-the-front-brake-lever-on-a-4-valve-bike#55591

If there is any sign of rounding out after removing the pin, don't hesitate to order a new one from BMW for about $20. Use a small torque wrench to tighten the pin (8 Nm or 70.8 in.lb.) - do not over tighten!

For those that don't do it, clutch and brake lever pins need lube, so too the clutch lever nipple and it needs lots of it.

Thank you, Olaf. The clutch is next then. As a side note, it looks like some BMW technicians are not aware of this either or do not care. It annoys me to no end when I pay top dollars for lousy service. It reminds me of what Robert Pirsig wrote about his experience with bad mechanics in Zen and the Art of Motorcycle Maintenance - dreadful!

ldescloi wrote:Thank you, Olaf. The clutch is next then. As a side note, it looks like some BMW technicians are not aware of this either or do not care. It annoys me to no end when I pay top dollars for lousy service. It reminds me of what Robert Pirsig wrote about his experience with bad mechanics in Zen and the Art of Motorcycle Maintenance - dreadful!

K bikes for a main dealer are old technology so main dealers are not the places to go to. Most techs there are born after the K bikes!!

Zen is good fun too!