Soldato
Well it worked. Took a bit longer than I expected with it not being a clean install. Ironically Paint.NET 3.5.8 was released yesterday so I had that ready to install. When I did get back into Windows Paint.NET installed fine but it did take an age to create the system restore. I was just about to terminate the process and try 3.5.7 when Paint.NET decided it was happy with the system restore it'd made and installed fine. FileHippo's Update Checker runs fine and Event Viewer is now working. W00t!Sounds like a plan Let me know if it fixes it (or not ).
Windows Update isn't quite going 100% but I think I can fix it. It's telling me that some updates are failing and I've added the three Windows Update URLs to the allow list so hopefully that'll work. I have a feeling I'll be doing Windows Updates in several goes and not a large single job. Since the repair install took longer than I expected I might leave SP1 for a while until I find any news on whether my problem is fixed, or even just has anyone else had it as well as me.
Cheers knowledge123 for your time and advice.