From Pete Roper:
"😁 The reason why you aren't finding the thin washer is because it was a much later addition to the gearbox. It only started being used about the time of the exposed driveshaft models like the Sport C and Daytona 1000 in 1995.
When assembled the splines that hold fifth gear poke through the output shaft bearing until they are essentially flush. On the early models there was not even an o-ring, just the stamped washer underneath the speedo drive.
Now by the time the 850T came along the stupefying 45 hp that could be delivered through the box worked the oil so hard it got so hot and thin that it started leaking past the washer and up the inside of the speedo drive in *Noticeable* quantities.
It wasn't really a problem as the loss was small and if you changed your gearbox oil at the advised intervals it was never really an issue. Being sealed to the swingarm by a boot the oil didn't leak out and make a mess, it just tended to eventually work past the UJ to shaft splines and dribble down to the bevelbox slightly overfilling that when it came to change time.
Because lots of fuckwits never changed their gearbox and final drive oil though there could be problems.
About the time the T3 chugged off the production line the factory started putting the o-ring on the end of the splines and then the flat washer was supposed to crush it and prevent the oil sneaking up the shaft. And it did! Sort of....! It certainly slowed it down a lot but the o-ring was still sitting on the end of the splines so, when crushed, it was only crushed over about half of the circumference of the shaft, so, sometimes, it would still leak a bit. Not enough to be a worry but when the exposed driveshaft models came along it could be messy and both owners and anti-pollution wallahs, rightly, complained.
So the final *Fix* was to put the thin, shim washer on top of the end of the splines. This gives a solid, flat, surface for the o-ring to be crushed against, finally meaning that the oil couldn't creep up the shaft and dribble down the back of the gearbox.
So! The long and the short of it is that neither the thin shim washer or the o-ring are vital. As far as I'm concerned an o-ring, (It doesn't need to be *Exactly* the size Guzzi specifies, in fact a slightly fatter cross-section is actually more likely to do the job!) is an excellent idea on any box but the thin shim washer is only really a good idea, (Even here I wouldn't call it a necessity!) on the exposed driveshaft models.
In reality, if you use some Loctite 243, (The blue shit.) on the threads of the output shaft nut when you tighten it it will perform 90% of the task of the o-ring.
Oh, and I see Pat Hayes, who is a top bloke, was just asking about this so please feel free to post my reply up on WG if you see fit.
Enjoy!"
