thomas went though this sort of...
It might be more cost effective for you to buy a whole new 23 spline dual adapter. the only thing different is the coupler.
If i remember right the coupler is pretty pricey though, so looking back he felt it would have been more cost effective to buy a whole new dual adaptor kit and then sell the old 21 spline.
Either way...
yeah the coupler is waay expensive! might as well buy a whole 23 spline adaptor kit
