I started the other thread on 5th gen charging problems a couple of days ago so I'm interested in your results. At first, from your description I would have thought that you had a second bad rr given that your voltage from the stator seems good until it's attached to a load but I found this snippet of information on a BMW site. It originally came from the Electrex site but doesn't seem to be there any longer and coincidentally, refers to VFRs! Anyway, after reading it, I think you should replace your stator and unfortunately, possibly your your rr as well as it appears that a failing stator will take out the regulator. Here's the quote.
<<VRF Regulator Rectifier Basics
Inside there is a six diode full wave rectifier, and every phase input can be switched to ground through a thyristor. The thyristors are switched by a regulator circuit that measures the DC output voltage. We call this a shunting regulator. It is a very simple system, and doesn't work very efficiently. But it does the job while not dissipating too much heat. That is why most OEM manufacturers still use this setup.
First of all the regulator relies on it's heatsink. That in itself is not bad , as long as there is good thermal contact between the diodes and thyristors inside the unit to the housing, and as long as there is a good airflow.
Quite often when a regulator/rectifier fails, a new one will fail after a fairly short time. It is a recurring problem (not on all bikes, but has been seen quite often). The stator has 18 poles, 6 per phase. Each pole has (I don't know exactly) about 20 turns of copper wire on it. Between the phase outputs of a delta wound system you will have 120 turns. Because of the hot spot in the engine, the copper winding's insulation starts to fail after some time. Most likely that will be somewhere from one layer of windings to the next layer on a pole. This usually happens only under load and when the unit is hot. Imagine a few of these shorts in between the phase outputs. You will have not 120 turns but say 50 or 60. The complete charging system will still be able to reach 14.4 V DC, it is rated for about 400W.
When you have a transformer with only a few thick windings, you will get a low voltage but higher current output. The same happens in the VFR Delta stator. Those 60 turns will give a much lower Vac but a much higher Iac. And diodes in regulator/rectifiers don't like high currents. If they are rated for 35 Amps, as most diodes are in this application, they can handle that whenever they get sufficient cooling.
When they run hot, the max current they can handle drops down quite a bit, which makes dissipate even more heat, and finally one of the diodes fails! Electrex stators are wound in star. The total power output is about the same as the original (lower Iac times higher Vac makes about the same... I know this is simplified, there is more to it....). But there are always two phases in between the phase connections. (=240 turns) The Vac is higher, and the Iac is lower. Even if there would be a short in between some layers of turns (I haven't seen that happen) you still wouldn't have the current output of the original stator, which is what destroys regulator diodes.
So far this is still unproven, but seems correct. It is difficult to prove, as you need to check the original stator for shorted windings whenever the systems is under load, and very hot. And it doesn't need to do it all the time even! Bikes that have had a few failing RR's stopped frying them after replacing the stator.
One last thing:
Problem #3:The output of the Voltage Regulator/Rectifier (VRR) is fed through the wiring loom and some sort of junction box to the battery. Make sure you have perfect connections here. I found a number of problems with voltage drops over these lines. Check the fault finding chart on http://www.electrexusa.com. It will guide you through the process. The best thing to do, if you see any voltage drops in between the VRR and battery (we are talking high current here, so any bad connection will give a significant voltage drop) is to feed the output of the VRR straight to the battery terminals using a (good quality) inline fuse.>>
Hope this is helpful to everyone.