Anybody on this forum had experience of this kind of bearing failure, as described on an overseas forum? Supposedly affects any Sportster engine. Seems like a major and potentially really expensive issue, but I haven't heard anything about it before:

"The main output shaft is hollow and carries inside 2 sets of needle roller bearings that in turn support one of the gear cluster shafts. Both the shafts therefore turn at different speed hence the need for the bearings. The problem is that the outer bearing is fitted in such a way that it gets little or no lubricant from the main box. This can result in the bearings failing."