1100 Wisdom
If the bike jumps out of gear, this can simply sometimes be that the gearbox oil needs changing (or that the gearbox is about to fail)
I don't reliably know anyway of telling how to check the gearbox with a test ride as (the earlier ones particularly) are very clunky anyway. Mileage is IMHO probably the best indication, that said, if there are obviously problems between 2nd and 3rd I'd suspect that (Mine stuck in 2nd gear immediately before it failed)
My first one failed (the original one) at about 93,000 kms, and now the replacement one (a brand new item, the latest part number from the later 1100) is now ageing a bit (187,000 kms) although changing the oil has helped it to stop jumping out of gear periodically.
Personally I'd be more concerned about the clutch, final drive, electrics and suspension than the gearbox when considering purcheasing an 1100 but that said, it's really a great bike if you can find a good one.
* Check the clutch by accelerating hard in 5th on the motorway, if it slips at all, it's on the way out.
* Check the suspension adjuster is not seized by trying to turn it any bounce it up and down a bit to see if the rear is leaking any oil
* Check the electrics around the ignition barrel, look for signs of wear where the steering movement has rubbed against the ignition barrel cable.
HTH
David