In service to WG as a technical resource, I thought it would be worth dropping a bit more info as a way of clarification. Seeing this brought everything into focus for me, so I'd like to share.
Several people in and out of this thread (i'm blessed with Guzzisti in my real world environs!) suggesting trying to get at this felled washer through the gear case drain hole. As Wayne Orwig clearly stated, that's simply not possible. The area of the case the washer falls into is entirely isolated from the rest of the gearbox by a bearing. This photo shows the relationship between the driven speedo gear, and the bearing:

If you can access that space from above, you don't need to remove the swingarm. I fiddled with any number of magnet/dental pick scenarios, and simply could not get down there. In the end, I spent more time trying to get at it from above than I did removing the wheel and swingarm! If I understood the anatomy better, I'd have saved lots of time.
Also, there is a ball bearing which rides in a groove on the output shaft. CRITICAL not to lose this.

Thanks to all for the assist. The MG Cycle got my seal to me in little more than 48 hrs from clicking 'process order', and it's waiting for me at home. Hoping for a test ride before dinner.
Cheers.
