maybe try riding with your lights on all the time might help, i know when they are not in use, the regulator grounds the charge coming to it, this of course produces heat, hence the fins on the regulator to get rid of the head, might also be worth checking that you dont have any short circuits in the wiring .
Riding with the main lights on does indeed give your "Shunt" type regulator a much easier time. Some stator / flywheel combinations are better than others. Some stators have thinner windings with more turns so they have stupidly high voltages when fully saturated. All this excess voltage has to get dumped through a Zener diode or a thyristor to ground. This situation is usually evident if the headlight is of good brightness at tickover. A series type regulator will solve the problem as it works the opposite way. Anyway... Riding with the lights on all the time is a bloody good idea and it acts as an automatic assistant regulator that comes free of charge. (Ok the occasional bulb replacement)