I'm going to recommend a clean reinstall (as my preferred option).
He has a lot of random stuff on his laptop.
I'd be surprised if he still uses all of it (he tends to install programs and then only use them once or twice).
It doesn't take that long to reinstall Windows and programs (and he has an SSD).
He just started 2 months Long Service Leave (that should be ample time).
If he doesn't want to do that, then I'll follow the "view the CBS log and replace the corrupt files" option.