Well, I finally got the nut off and removed the NSS. I think a previous owner tried to remove the NSS and stripped the threads halfway up the shaft.

Anyway, I was able to get a putty knife between the nut and washer, and applied enough pressure, that it finally caught some threads.

The back plastic had a crack clear across it, so I just ordered a new NSS.... $45.00 at usautoparts.com

I got the part today, and installed it easily. I now have reverse lights, but I was hoping a shifting problem would miraculously disappear too..... but no such luck.