As I said the Austrian company which did the stator rewinding does not exist any more. So I asked a few guys I know, about the problem and possible solutions. After a hint I read a zillion posts in German and even Italian forums. Most things are not new but I think worth to mention even if there is no demystification.
At least we are not alone and there are hundreds of Aprilias having the same problem. There are similarities, no doubt. The F8 engine and the Aprilia V2 are both manufactured in Austria at Rotax (lets see if I can get them on the phone, maybe I will try). This allows to speculate about which supplier Rotax uses for the stators of both engines. I'd guess the same one (Denso). Many, many Triumphs and Buells (Rotax engine!) have the same problem, but thats another story.
Now it is getting complicated as I have to talk about things I am not really familiar with nor do I fully understand them or have more than basic knowledge necessary to see the potential relationships. Additionally my English isn't the best. So please forgive me if I explain or describe technical things a bit odd.
Before I write anything else, the German Prilia riders have for their understanding solved the problem. More or less.
Many Aprilia stators may have died due to a loose conncetor or cables which have been crimped too loose. If I understood correctly the loose conncector/crimps leads to a power interruption and that - so was said - leads in DC systems to an arch (spark) which can create superhigh voltage for the fraction of a second leading to a electrical discharge between the windings of the stator.They named it Tesla - effect. Changing the lenght and the connector sitting in the engine cover cured this and less alternators died. But this was not the major problem as further rotors burned and - guess - with higher mileage affected the far most Aprilias.
For most bikes the problem is heat.
And no the problem is not heat from the exhaust! I am pretty sure you can forget that as the Aprilias exhaust isnt close to the engine cover where the stator sits. Aprilia uses the same type of regulator as BMW does, so it is in fact that system you (or somebody else) described in that way that the alternator is always working with full output whether the produced electrical power is needed or not. Maybe not the best of descriptions but the way I understood it.
Well, the Germans went exactly the same way and even contacted the same companies like CARMO in the Netherlands for rewinding and for different types of regulators.
However, if I translate correctly it was said that the Aprilia (like the BMW) uses a cross regulator with shunt and with such a system the excess energy produced is converted into heat. Heat which affects the rotor. So the guys talked to Carmo and tried different regulators, like MOSFET cross regulators, Harley Davidson regulators and other stuff.
They ended with regulator rectifiers they got from Cycle Electric Inc (Series E 600) or Compu-Fire (55402). At the end a long term solution was to install a Carmo rotor (with different insulating) together with the Compu-Fire regulator. Some guys did only install the Carmo rotor but they soon were roasted too, it was said that some of them died between 700 and 5000mls. Most guys who installed both, Camro rotor and CF regulator had no problems, one reported that everything works fine since 5000mls and he checks current, voltage and other values regularly but did not find the slightest problem.
Its for sure that the regulator alone is not the problem! The Germans also assumed that when magnetism of the permanent magnets is set to high ex factory the electric power is too high resulting in a higher temperature of the stator coil.
One guy posted an image showing the differences of a MOSFET regulator (Yamaha R1) and the Compu-Fire 55402)
Last and maybe most intersting is, that the Italian Aprila riders started some kind of protest action with forms one could fill on a website and send directly to the Aprilia factory. The Italians reported that Aprilia started slow but then further investigated resulting in a reduced price for the stator and after a while in changing the output power from 500W (watt) to 300!!!
Needless to say that Aprilia never made an official statement, they see no problem at all!
Aprilia Italy reduced the price for the rotor dramatically and stated that the warranty for replaced stators is valid and extended if full service documentation is existing. Germany followed this procedure described in Aprilia Service Bulletin #006/2011.
Well no really new findings, but maybe good as food for thoughts.
PS. I had technician from Bosch on the phone a minute ago and he said if you measure 100°C (dunno what Farenheits that is) on the engine cover the stator itself will most likely have over 100°C which he thinks is the treshold between normal and too hot. Exceeding 100° he said, will damage the insulating of the wires. Not if this happens once or twice or even ten times. The insulating is killed by the cool/hot/cool cycle. The insulating coat (similar to some kinds of paint) gets softer when hot and when cooling down gets hard again. This cycle, in his words, lead to microscopically small cracks in the insulating. It gets brittle (hope that is the correct term, am not sure).
PPS. Hope this helps, at least it took me two hours to write this sittiung between 10 different dictionaries