I thought I would post my experience with the good ol loose final drive nut. 'bikemad' did a good job reporting, but mine was slightly different. Mine happened at 149,100 kms. After this many K's I never thought it would happen, so just be mindful that it can happen at any time.
I heard a faint knock, and vibration just as I was pulling into Iguazu Falls (Yes I am Bragging). Turned it off and forgot about it. Came back a few hours later and rode off as normal forgetting about it. It was then clattering like a bastad. I nursed it 10 miles back to the hostel having a pretty good idea what it was. I tried 'bikemads' method of holding the front brake and loading it up but it made it better? This made me nervous that it wasn't the 'loose nut' as this method was supposed to make it worse!
I pulled the cover off and hoped for the best/worst?
I didn't remove the foot peg, but i did remove the two allen bolts that hold the rear brake slave cylinder on to drop the brake pedal down and give me clearance. I also didn't remove the clutch cover to remove the crankcase housing. Don't do this! You will never get it all back on in one piece. Easier to put them back on seperatly.
Luckily for me it WAS the loose nut and lucky for me the local Yammy dealer in 'Foz de Igaucu' had a crankcase cover gasket in stock. I also befriended 'Rod' who organises the local 'Horizons Unlimited' meetings down here. He is friends with the dudes at Yamaha and we managed to borrow a torque wrench and 36mm socket off them.
I re-used the old lock tab as one side was unused and they didn't have one in stock anyway. I had to use gasket sealer to glue the clutch cover on with as it ripped in half when i removed it. So my advise is get the 2 gaskets ordered up before you start.
Torqued it up to 120nm by stuffing rag between the gears to stop it moving. A trick i used to use when I was a car mechanic.
Got it all back together after 76 attempts to align the poxy clutch back into position. Sounded good and felt strong after.

Time to strip the engine, in a Brazilian Hostel-


Crankcase cover off in one piece, stupid idea-


Removed with fingers, No Bueno-


Its good to have friends that have friends of friends-


It be a 36mm I tells ya-


Stuff some rag in the gears to lock them up when torque-ing -


Where's my apprentice when I need him? Gotta love gasket cleaning -


Nearly back to normal-


Its all good, LETS RIDE !

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http://advrider.com/forums/showthread.php?t=988891 'South Dakota to South America'