There are some really lousy-quality imported regulators on the market now, so getting three bad ones in a row doesn't surprise me. Have you had any of them apart, at least removing the cover? Some of the repops are actually solid-state items with few, if any mechanical parts, while others are just cheap-quality mechanical regulators with springs and points inside like the originals. Some of those will respond to adjustments, but it's better to start with a good-quality original-equipment item.
Jerry
