(Like many of my technology postings, this is really here for my own notes on problems I run into, the solutions I try and what works when. They are updated as I learn.)
I'm gonna get me a degree in Microsoft Error Codes.
So it seems that error code 0x80070643 is a general error code so what work here might not work for everything.
Oh look at that! I ran the Windows Update Diagnostic, ignored "Potential Database Corruption" and reran the Updates. Worked.
Solved! (for now)