I used step 7 in brink's tutorial, the command:
Dism /Online /Cleanup-Image /RestoreHealth /Source:esd:E:\Sources\Install.esd:8 /limitaccess
where the downloaded iso was mounted as E on my system and I'm using win10 pro (index=8)
But did not see a change to my symptoms after rebooting and re-running WU
So I googled my WU error message given to me by tray notification and got to this page.
Fix Windows Update error 0x80070003: 5 methods that really work
It lists several things, all of which I had tried already except for deleting two folders within the softwaredistribution folder. So I deleted those, restarted and retried WU, to no avail.
Then I got to thinking maybe the issue was something I had modified with winaero tweaker, so I reset all winaero tweaks to the win10 default state, rebooted, re-ran WU, but that did not help either.
Then I recalled how I have at times changed the permissions of various folders, so I used the Subinacl tool to reset all permissions to their default, using the below cmd file I found posted somewhere.
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subinacl /subkeyreg HKEY_LOCAL_MACHINE /grant=administrators=f
subinacl /subkeyreg HKEY_CURRENT_USER /grant=administrators=f
subinacl /subkeyreg HKEY_CLASSES_ROOT /grant=administrators=f
subinacl /subdirectories %SystemDrive% /grant=administrators=f
subinacl /subkeyreg HKEY_LOCAL_MACHINE /grant=system=f
subinacl /subkeyreg HKEY_CURRENT_USER /grant=system=f
subinacl /subkeyreg HKEY_CLASSES_ROOT /grant=system=f
subinacl /subdirectories %SystemDrive% /grant=system=f
----------------------------
As those lines were executing I would say about 1/3 resulted in a successful modification of permission, and 2/3 did not, showing an "access denied message" instead. No idea what to make of that. In any case, a reboot and re-run of WU still is unable to complete the update installation.
The system still works fine, however am still unable to install this update successfully. sfc scannow produces no errors, in case I forgot to mention that.