that is what my mech put in my bike. Manley Cycle is pretty reputable, and I dont think that they would do their customers wrong. Not trying to say you are wrong Scott, maybe there are advantages to the different weights. Also I went to the local Duc dealer for some oil and that is what they said I should be running. Maybe it has something to do with altitude and temperature? I dont know. Just pulling ideas out of my butt right now.The 20W50 is not energy conserving. 8)
...the 10W (low temp viscosity, W=winter) is not enough for the transmission but would be fine for the motor.