It almost makes my blood boil to think about it. I have no more 6 volt tractors on the place because of junky regulators and the money I wasted on them.
The only thing here that has a regulator on it is the grain truck with the 12 volt genny. When that thing gives me fits that is getting an alternator, too. It is the original so it should outlast me. Unless someone does a little "midnight auto" to use on their equipment - that's about the only way to get a good one!