The bearings themselves are OK it is the almost non-existent amount of grease that Yamaha apply on assembly that's the issue. Most of the damage gets done before the 12K service which when the dealer should re-grease, by which time it's too late. I bet if you replace them with same OE parts and grease them generously yourself, they'll way outlast the first set put in at the factory. I strip and grease every 6K, rather than just "check" as the service schedule says. As Tony says, it really doesn't take that long once you've got the hang of it.