*&^%$*(&%$. It seems that the local dealer'* mechanic who greased the shaft before obviously used an impact gun to reinstall the bolt since it is now rounded. I tried 12mm 6 point and 12 point sockets, a 1/2" 6 point and even a 12mm box end, none of which fit on the bolt head.
This will be an interesting discussion with their service department. I'm not too fond of them to begin with since it took 6 tries to stop water from getting in the trunk and when it was fixed, I found that they had given me the car back with the spare tire well full of water. Dimwads.

I gave up and put everything back together. I'll be talking to the dealer this week because even if Sears does have something that might work, in my opinion, if the dealer screwed it up, they can fix it.
When you think about it, none of us should be having to deal with this whole crappy shaft issue. Quite honestly, with as much as has gone wrong with this car since it was new, I'm starting to lean to the dark side, aka something Japanese. I have been a loyal GM owner for nearly 40 years and this has been the most disappointing car I have ever had. I understand that any manufacturer, including the Japanese, will have bad cars from time to time but most of the problems in the Bonnevilles are just plain **** poor design on GM'* part.
Rant off.