Seems not to be your RR then, but just a note about Electrex RR851 - it is a 'series' regulator, which means that instead of fully loading the stator coils all the time like a 'shunt' ( parallel) RR and dumping excess current not used by load as heat the 851 'series' one actually has a regulator in 'series' with load - this means it only draws enough current from stator to satisfy the load, I fitted one last year to my AL7 and did some test of heatsink temperature - the original Shindengan heatsink ran at over 70degC and the Electrex one ran 30degC cooller ( on same day at same ambient temperature ). I am not able to get a temperature for the stator coils, but being a lot more lightly loaded they have to be running considerably cooler. At the same time I fitted a digital voltmeter to handlebars, I found that when I ran feed to digital voltmeter from sidelight bulb ( on all the time ignition is on ) I was getting a reading 0.4 volts lower than when I ran feed straight from battery terminals ( voltage drop in the connector plugs and wiring ) - now it is 14.4v to 14.5v all through rev range.
https://www.electrexworld.co.uk/acat...Rectifier.html