A guide to how screwed your bearings/sleeves are, from 'fine' at left through to 'knackered' at right.
The left hand one I actually changed about ten thousand miles back. If I wasn't shipping the bike several thousand miles to a country it's not sold in I'd not be changing it.
The right hand one is actually from the swingarm pivot. While I've regreased the linkage bearings a couple of times, the swingarm hasn't been out since it left the Yamaha factory. You can actually feel recesses in the sleeve where the rollers have sat.