Except they DID solve the issue, though admittedly after some cameras had replacements with the same potential failure as before.
All newer repaired M9 sensors from Leica are corrosion-free. Anyone who owned the M9 and didn't get it replaced with the newest sensor that will not corrode has themselves to blame, except maybe the rare case where they thought it was the newer version but wasn't.
Truthfully, Leica should have never replaced a sensor till the problem was eliminated, or put you on a wait-list to get the newer sensor, but oh well. I can think of one person who had no idea the problem existed until I mentioned it, and they found corrosion on their sensor sometime later, but I think that's a rare case.
I kinda miss my M9 sometimes but ultimately I'd rather shoot film.