Thanks Jon, I did try that without much success. Difficult to do properly in situ, also difficult to set up with a digital meter. I'll have a proper go when I have replaced it and aquired a decent analogue meter. There's an interesting article here REPAIRING_THE_STANDARD_RB106. In particular the addition of a diode to reduce the regulator contact arcing and burning is an interesting mod.

1956 Plus 4 4 seater