Had mine go a couple of months back. Initial signs were notchiness changing down from 4th to 3rd. Then it became more reluctant to change down from 4th to 3rd until I had to clutch in, wait a sec, pressure on gear lever, blip throttle, gear drops in as revs match, clutch out. All a bit distracting. Then it started to do this on every down-change. Later up-changes got notchy as well.
Got a BMW mechanic to ride the bike. He came back and immediately asked the parts guy to get a new gearbox in.