If it were the compensator you wouldn't have been able to drive 90 mins to the dealer without a very obvious rattle at idle and low revs.
It's almost certainly the rectifier and as Rog says, replace with the Harley style unit.
Also check the battery, the standard Banner unit is not sealed for life and needs topping up with distilled water from time to time and will only last a few years anyway.
Again there are better ones listed in the Alternative Parts List:
https://www.mtwc.co.uk/wp-content/uploads/2018/09/M3W-part-numbers-V2-Word-200918.pdf
