I see no evidence of moisture damage in that photograph. There's some gunk on the metal frame, but that looks more like glue that holds rubber seals in place than oxidation damage. Titanium dioxide is white, not black or green. However, if the metal frame is corroded, I suspect that it was corroded before they assembled the camera at the factory, because I see no evidence of water damage to the electronics at all in that photo.
Hi dgatwood, I just checked specs, as I thought the body is quoted as made from magnesium, however pure magnesium is highly reactive and is quoted in one article as "not generally used for construction" no idea whether that means cameras or not!
It states that most likely it is an alloy of magnesium which would generally corrode to a gray film coating but should be protected by a surface treatment.
It also states that corrosion due to pure water increases With temperature, no mention of what temperature, but it also says the alloy is not structurally affected until temperatures of 95 to 120C.
The greenish colour would indicate to me a compound involving copper was involved and as this is on the body of magnesium that would be unlikely so I guess that just adds to the confusion, I would think it is unlikely to be contamination from copper of the pcb as that is lacquered over to prevent corrosion so we are left with plated contacts to corrode.
Also as I have said in previous posts part of my expertise is classic cars, I have bolts of approximately 40 years of age that have been left in containers that have collected water sufficient to cause a tide line. Yes some of the bolts have rusted, generally those with tool damage that has damaged the plating, but many have survived so clean they look like new. It is so unusual to find tool damage on fixings inside modern electronics that I would not be surprised to see no corrosion on the screws.
However having said all that I am with every one on your main points that it should/could not have happened so quickly and that it could have been either sweat or condensation "pure water".
Most of all I would think that this could be a warranty situation as a seal failure would seem to be a real likely cause of this.
My deepest sympathy for your situation.