WMI repository broken (already tried several solutions)

I've done a clean install of Windows 8 and updated to 8.1 via the store update on a new SSD about 1 month ago.
Everything was fine back then. Regarding hardware or settings I've changed nothing since then.

Since about 1 week I've got some serious problems related to WMI:

• event id 28
  At each system boot an error of event id 28 gets logged which points at the WMI core components.
  Seems that the WMI-Installation is somehow broken.
• event id 3
  As a consequence of the WMI error windows security center reports this error. Seems that windows needs WMI to check for running antivirus programs which fails. This leads to a notification in the taskbar which tells me that there is no active antivirus software (which is wrong).
• event id 43
  Furthermore I get this warning which says something like "there was an connecting to namespace "\\.\root\cimv2" through WMI: 0x80041001" (translated from german)

As a sidenote: the WMI service is running at startup and can be turned off or restarted with no problem.

I concluded that the problem must be WMI, so I tried to fix it:

• WMI repository (refresh via commands)
  winmgmt /resetrepository or winmgmt /salvagerepository didn't help
• WMI repository (manual refresh)
  Renaming the repository folder and let windows recreate it after reboot didn't help either
  
  I also found a batch script that should recreate the repository which also didn't work.
  (some for-commands for every dll, mof and some other file type; can't remember exactly)
• System restore
  Gives me an "unknown error at system recovery" 0x80070057.
  Although I don't think this would help much, as I've only got 1 restore point thats about 2 days old.
  As I've said earlier I didn't change anything os wise.
• System refresh
  Prompts me to insert an installation medium which I don't had in the first place (as stated earlier I bought windows 8 on disk and updated to 8.1 via the store update, so I don't have any disks for 8.1).
  
  So I downloaded the ISO for 8.1 by exploiting the windows 8 downloader glitch (cancel download for 8 and then start downloading 8.1).
  
  Even with this ISO I still could not refresh my system - got an error which I don't know anymore.
• WMI connection
  I also found a command which opens a tool where you can try to connect to the WMI repository.
  This gives me the same error as stated under "event id 43" (see above).

Are there any other ways to repair WMI or the repository?
I don't want to do a complete system refresh again since the system otherwise runs perfectly fine...

Would appreciate every tip you could give me!
If you need some more details or system logs just ask for it and I'll provide them!

PS: Please bear with me that I can't give you full details on every solution I tried... I did this at 3 o clock in the morning and forgot to take notes / make screenshots of everything.

No one that can help me here?


Edit: Just ran sfc /scannow and attached the cbs.log to this post.

Edit2: I also did a reboot and exported the eventlogs that show the errors I get.