I removed my Stelvio front wheel and during that simple process, the axel spacer fell out. Just to be certain, I checked the Guzzi parts manual to see which side it's supposed to be on. The manual is clear that it's on the opposite side from the ABS ring and the opposite side from the threaded end of the axle--clearly, the left side is where it goes.
Nope; that's not playing.
I checked leafman60's installation guide from 2012 and he makes clear that it goes on the right side (flange out).
And, so it does. Thank you, leafman60 (and thank you Luap for the search box). It's perhaps a small thing, but that's what makes life better.