Bill; Yamaha uses now and I believe used, 20 yrs. ago, a cast collar and mounting plate. The stem is usually the cause of these problems. They develop cracks or splits and cause the symptom you describe. The only way to fix the problem is replace the caster. Replace the full set while you are at it, doesn't involve that much extra time and saves the customer aggravation and money in the long run. Good Luck. Jim Bryant (FL)
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