I removed the trim wheel and gearbox assembly from the airplane to examine it. The steel trim wheel shaft runs through a hardened brass bushing. In my case, both parts were worn causing the wobble. The service manual doesn't mention lubricating this part -- probably because there really isn't a good way to lubricate the bushing without removing the chain, driving the roll pin out of the sprocket and removing the trim wheel/shaft and applying grease. A better design would have been to use a standard size oilite (oil impregnated sintered bronze) bushing. I ordered a new shaft and bushing and plan to drill a small hole in the top of the bushing. That way, at annual I can remove the plastic chain cover and pump some grease in with a grease needle.
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