Thank you. In my response to you, I had said that BMW was sloppy in design to allow partial disengagement of the spline, but what I hadn't said (didn't want to sound like BMW bashing) is that the really sloppy part in the design is to allow any sliding movements at all in load carrying surfaces. Good designer consider this to be quite taboo, IF it's at all avoidable. Take a look at how many generations of people had gone to the trouble of trying to design the "perfect" gear tooth profile so that it achieves perfect rolling action while meshing, instead of sliding action. In practical life, that's impossible to achieve, but we are very close to it. The actual meshing action is mostly rolling (no wears!), but also a little slide.Speaking of facts, I have been wrong in regards to the drive shaft sliding on the spline on our bikes
"Normal" drive shafts, such as one on a rear wheel drive truck with traditional rigid axle/leaf spring suspension will slide as the distance changes, like a triangle, but because BMW uses paralever, the distance between splines relative to one another do not change, well not significantly anyway. So the lubing is simply to prevent corrosion.
A glaring example of where sliding action is totally unavoidable is the piston rings sliding on the engine's cylinder wall! That is unavoidable, and if you can find a way around that, you will be very rich! It is the weak point. Look at the Wankel engines. Fantastic power plant, IMHO, but it didn't catch on. Why not? Frequent seal failures! Small seals sliding continuously on a surface.