MB.........
I hate to tell you but I believe the only fix is a complete format of the hard drive, and a clean install. I don't know for sure, but I think there was something corrupt in an update prior to Windows Update KB2919355 that keeps it from installing, and the only way is to start over. You are correct that you will have to reinstall all software, and any specific customizations you have, but if you back up your files on a separate hard drive it will most likely take less time than you have already spent trying to fix this. As irritating as this is considering the only thing we did wrong was install all updates as they come to us, and although I think the engineers at Microsoft should be able to create an update that identifies the issue and fixes it, I don't see that happening. It took me about 30 minutes to format and do a clean install, and then another 2-3 hours for all the updates. After that I don't have a ton of customized stuff so the rest went easily.
I know it's a pain in the ****, but it solves the problem!!
Good luck,
Jay (Still prefer this to selling my soul to Apple)