overvolts on G model

[sunnysky]

sorry to bring Alternators and overvolts up again but need some new ideas.
I have a G model with the two regulators (one for each engine)
occasionally Im getting the overvolt situation with both alternators shutting down and red overvolts light on.
Sometimes say on a two hour flight 5his can never happen. Other times it could be three or four times.
I've tried running on Front alt only and it NEVER happens.
But it does on Rear alt only, same as with both running.
I've tried swapping regulators but it does not transfer the fault.
I've checked alternator voltage and it seems correct. around 28 with both running under losd add 26. 5 ish on only one alternator. Both regulators are the solid state Zefftronic/Electrodelta type with no adjustment.
where now too look. I had the diode board changed some years ago and physically it looks ok
Anyon3 had the dame issue on the G model pleaee and how did you eventually resolve it ?