OK, I'll take the bait.
To my somewhat limited understanding there are two reasons to grease the splines on our bikes.
First is to prevent sliding wear on the faces of the splines. This is most important on the spline joint going into the final drive. Dry splines will wear, opening the clearance between the inner and outer splines. A thick grease in this joint will also act as a cushion for the impact loads imposed by rotational speed changes. As the clearance opens up the impact loads on the faces of the splines increase and they will start to be peened back further opening up the clearance until enough of the spline is worn away that no torque can be transmitted through the joint.
This is apparently not an isolated failure as evidenced by the number of reports of it within even this somewhat limited community.
Second is the clutch. My understanding here is that lubing those splines is more of a drivability issue. Dry splines here affect the disengagement of the clutch and thus the ease of shifting. I have heard that dry splines can make downshifting difficult. On both of my bikes I did the clutch splines as part of my initial commissioning prep work and so far both of them shift smoothly and positively.
As far as frequency, I plan to do the final drive on my bikes every winter when they are off the road, and will be doing the clutch every two or three years, probably on a 20,000 mile interval. I suppose the splines could be ignored, but the cost of a failure is a lot worse than the time involved in preventive maintenance. And as I mentioned earlier in this thread, stuff like this is more like foreplay to the pleasure of riding these wonderful machines.
