Hi mauifrog! I am trying to update the wii to 4.2k as you suggest.
I am using System-Update_4.2K archive you posted, and when I open wiiscrubber I get warning: 'Doesn't seem to be the correct key.bin'. This is normal I guess, so I click "yes".
Which is the right procedure to replace the Update partition in a ISO? Should I use a Korean iso or a PAL one is also ok?
For the moment I only got iso files without an update partition, so I don't know if I can create a new one when only "DATA" partition is there.
Thanks for your support!