Microsoft update (MSU) does not find updates for other Microsoft products (e.g. Office) after MSU update

I found an answer to my own question. I am running Office 2010 ("version 14.x"). To enable updates again proceed as follows:

1. Close all running Microsoft Office components.
2. Open Regedit
3. Go to HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Common\General
4. Modify the "ShownFirstRunOptIn" value from 1 to 0
5. Launch a Microsoft Office component, it will give you the option to download the updates, make sure you select it.
6. Done. If you go back to "Windows Update", then "Change Settings", you will see the "Microsoft Update" and "Software notifications" sections are available again (until the Microsoft Update check box is unchecked again).

The key in step 4 might have slightly different names across office versions. In my source the key was called ShownOptIn under office version 12.

Following these steps also MSU shows the missing checkbox again and it finds all updates including updates for non-office products (e.g. Silverlight)

It seems that when the Microsoft update servers are under heavy load, e.g. Patch Tuesday or shortly after, searching at the same time for updates for both Windows and MS products (such as Office), can cause various error situations to arise. Unlinking the search for MS Products, so that it only looks for Windows updates, then has a higher likelihood to succeed. It is only unfortunate that Microsoft has made it so difficult to reinstate the search for updates to its products.