5D MKIII light leak.....Just how serious of a problem isit??

[Rocco]

If Canon is offering to fix the problem I would guess they think it does effect the ability to get an accurate and consistent metering for exposure, and they feel it may be nessesary to fix it in order to reduce variablity in some instances.

It may be that from a PR perspective, it's simply worth every penny to offer their customers peace of mind. It is a lot of money to spend on a camera to have a problem like that. One that's vague in it's actual impact. And you're right, I don't think anyone has had the brass to test and see if the issue affects weather sealing.. (anyone want to volunteer?) Though, I'm sure Canon R&D did weather sealing tests before settling on the final design. Maybe it was simply a manufacturing problem after the fact.