They are not greased well enough in the factory.

Replacing is a lot of work, but not too difficult. Take out front wheel, forks, steering bar, triple clamp nut, top triple clamp, retainer under top triple clamp. Now you can take out the T-piece. Removing the bottom bearing is a ****ty job, your dealer can help. Taking out the race can be done with a large flat piece of metal. Put it on top of the bottom race and put pressure on it . It can take a lot of wiggeling but eventually you will win. The top bearing is easy but did not need replacing in my case.
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