Error: 0x80073712 when installing KB 2919355

Ok win 8.1 installing in a non destructive manner right now -- I hope.

So after this, you're saying I need to complete the steps you previously outlined still before attempting 2919355? Just want to make sure :)

It'll work great =]  for future reference, in case you have to do a repair install again, if you don't have your activation key handy, you can use what Microsoft deems a "generic key".  Essentially, when Microsoft changed their licensing structure from 3 PCs to 1 PC, they also changed the setup to require a PK before you install, so they created generic install keys for all versions of Windows 8 and 8.1 that are public and can be found by googling your windows edition followed by generic pk or product key.  Once you sign into windows with your microsoft account, you'll need to go to pc settings - activate and enter your activation key. Either way works fine.

Once you repair your install, and once steps 1 - 5 are completed, run disk cleanup, select the system files button, then when it reloads, select all boxes and delete (make sure it's after step 4 as it deletes windows update files, which is where DISM and SFC pull files from to replace.  You'll also need to reconfigure System restore as most times the repair install turns restore off since its the simplest way to delete all restore points (which is a must upon an OS reinstall/install).  You may need to turn it back on via the configure option on advanced system properties/system protection.  Steps 1 - 5 deal specifically with the component store corruption.  The 2 steps under "second" are to essentially reset windows update.  You'll be able to install every update, except 2919355.  If you want to attempt continued troubleshooting and trying to get 2919355 to work, just make sure you create a restore point before trying to download 2919355.  This should at least prevent you from having to do another repair install.  If you do choose to continue troubleshooting, I would recommend running a restorehealth command every now and then to make sure any corruption isn't preventing it from working.  This may also help you to narrow down what causes the fatal corruption to the component store.  (In reality, there should never be corruption so great it prevent dism from repairing the component store as you're able to point to where you want the source of those files to be pulled from. By default, they're pulled from windows update, however by using the /source command, you can point to the windows installation media by mounting the install.wim (once converted), and DISM "should", being the operative word, be able to repair the component store... not so with whatever corruption Windows Update causes while downloading/installing KB2919355)

Any non microsoft antivirus/firewall will need to be uninstalled, computer restarted, then reinstalled.  Before you do, export or backup your settings for those softwares (there should be an option somewhere to backup your custom settings and firewall/antivirus rules).  Certain drivers may need to be reinstalled.  If you use Intel wireless software, that will most definitely need to be uninstalled, then reinstall (although you may be able to get away with repair, which is accessed by programs, then when the list of all installed programs pops up, right click on the program and select "change". If the application has a "repair" option, it will show up, if not, just uninstall/reinstall.  **Always remember to restart your computer after every application/driver install**  There may also be some applications here and there that may need to be reinstalled... itunes is usually one, as it stores dlls in the windows folder. 

You may know this, but in case you don't, a repair install via the upgrade option of your current installation replaces most OS files, if not all OS files, contained within the Windows folder and I think certain OS files within the program folders, though I could be wrong on those.  That's essentially why it fixes all windows file corruption issues and is what Microsoft should be telling end users to do, not reset/refresh, thereby creating a big problem and inconvenience for the end user.  You'll ,probably need to do a repair install again at some point, so if you have a large HDD or space you can spare, I would copy the entire disc to your documents or downloads folder... somewhere that's not on the C: drive.

Two suggestions that will save you time in the future:

1. once you get your system the way you want it with software and settings, take a wim of your drives (using dism, NOT imagex, as imagex is not compatible with Win 8) You will need to boot from a WinPE USB Drive.  This tutorial is the best for creating a basic WinPE USB drive: http://reboot.pro/topic/19156-create-a-bootable-winpe-50-x64-usb-drive/ And here is one that's a bit more complex, but runs a full gui of windows 8 within the PE [Pre-installation Environment), allows you to add extra applications, and do multiboot from the USB Drive (say 1 option for WinPE, another for Hirens BootCD, another for an Acronis Recovery disc, etc.): http://w8pese.cwcodes.net/  

If your familiar with WinPE, jump right into the latter one, as it's an installable program that allows you to customize every bit of your WinPE drive.  (If you're not familiar with PE, I would recommend the basic tutorial first to build a basic WinPE drive, as it also helps with muscle memory for the DISM commands and gets you familiar with WinPE options and components.  The one thing the application in the latter requires is for your to convert the install.esd within your installation sources folder (i think it's sources at least) to a wim file.  This is where it gets a bit tricky:http://www.tomshardware.com/faq/id-1868563/convert-windows-install-esd-file-install-wim-windows.html

One final thing I would recommend is defragging the system drive with Contig from sysinternals.  It should come with a gui, as well as command line, however, if you can't find the gui version, let me know and I search my bookmarks for it.  The GUI works better than the command line, which i've found to be a bit temperamental.

Also, to avoid activation key lockouts [where you have to call in] due to activating windows on the same pc after a repair install (if you have to do additional ones in the future, as microsoft literally means 1 PC, 1 activation) it seems to help if you keep the name of your pc the same.