Mopar 8.75 posi. wont work. Why are there 2 rows of spline?

How do I know if I have the rebuildable spicer? and who do I contact to rebuild it besides someone in my area? Darter6 you said you called Dr. Diff, is that just a generalization to someone who works on these or is there actually someone I can contact?

thanks again guys, this is really helping me out!