After a month or more of trying all the standard fixes I was finally able...
In the Registry Editor (click the Start Menu icon and type regedit), go to this location: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\WIMMount
FIrst thing to do is make a backup of this entry in case anything goes wrong. Right click on WIMMount and select Export and save the backup somewhere.
Now click on the top level WIMMount entry (if you expand it you will see Instances and WIMMount sub-directories but we will not be using those) and in the right side panel you should see 11 or so entries.
Find the entry with the name "ImagePath" and make sure the Data column shows this: system32\drivers\wimmount.sys
If it does not say this, click on "ImagePath" and change the Value data field to system32\drivers\wimmount.sys
In my WIndows 10 registry, this entry showed something different so I changed it. I confirmed this entry on my two other Windows 10 PC's.
Finally, check to make sure the wimmount.sys file is in this location: C:\Windows\System32\drivers\wimmount.sys
Source - https://docs.microsoft.com/en-us/answers/questions/55836/windows-update-failed-error-0x80070003.html