Some 300's 400's had a loose bearing fit (tolerance) between the steering knuckle and the wheel bearing. It makes a clicking sound when turning (usually).

Kawasaki has been telling people to use loctite to fix it. Remove bearing, clean surfaces to be adhered, and liberally apply loctite to outside of bearing and inside of knuckle where bearing fits. Let it cure before reassembly. Use the strong cylindrical part retaining stuff, not the medium strength or light stuff. Loctite 638 is the high strength retaining compound, so use 638. 680 is high strength for large gaps, this is not a large gap so that would be your second choice. The red high strength threadlocker would probably work if you could not find anything else, but even 609 general purpose retaining is probably better than using threadlocker.

Removing the bearing requires removing the tire, axle stub nut, caliper, spindle. Remove the knuckle from the quad to make it easier if you want. Take the circlip out. Drive bearing out with a socket and hammer. You may have to use an impact wrench to get the wheel off, since the studs don't bite into the spindle very well on some models. I welded the back of the studs to the spindle. Worked out extremely well.

This fix has been working very well on most machines, but some people have reported that the problem comes back. We really don't know if the bearing was cleaned well or if the mechanic neglected to use Loctite 638. Replacing the steering knuckle appears to be the best solution. I replaced a 99 P400 steering knuckle, and the replacement had a very tight bearing fit. Difficulty rating 4.5 out of 10