I too have a new 06' M7 with just 150 miles on it. The speedo stopped working on my last ride.
The dealer said that it was most likely the sensor, sometimes they just loosen up allowing the sensor to pull away from the gear case. You could remove the drive and check the sensor to see if it's loose, if so just push it against the housing and put a dab of silcone adhesive behind it. In my case the sensor was defective, so I replaced it and I added some silcone on the backside to keep it in place. I agree it's a good idea to inspect the drive while you have it out on the bench.
Becasue of my low miles I elected not to split the cases, instead I pulled both drain plugs (one at a time) and inspected the inside getting a small look at the gears and oil. Look for any signs of metal in the oil, of course the gear box should spin freely by hand. I would also recommend using new 5/16 loc-nuts to secure the gear box back onto the chassis.
Good Luck!
