A. Gunk. Carb Cleaner. Kerosene. White Gas.
B Not much. But you got the new Brass style - those shouldn't be as delicate as the aluminum ones. I do it by feel, so it's hard to put a ft/lbs figure on that. I'd go light on the torque, and if it leaks, snug it up a bit more. It's easy enough to reach when the bike is all together.
C. The gearshift seal needs to be pulled out - it won't just fall out. Remember how deep it is and press the new one in about the same.
Wanted: Dead, smashed, crashed or trashed gauges
BMW GAUGE REPAIRS - TACH*SPEEDO*CLOCK*VOLT METER *PODs & LIGHT BOARD*