Canon's fix for the 5D mk III light leak issue is a bit of black tape.

Roger Cicala frm LensRentals com investigates and explains:

"Let me say it here first: I knew this was going to be the fix since the first time I took one apart: Canon has this very cool black tape they used to cover circuit boards (I’m assuming

either water resistance or electrical shielding or both) and I figured they’d just slap another piece over (or under, depending on your point of view) the top LCD light. Which is exactly what they did. Yes, I’m making fun, but it’s a perfectly good solution and it works flawlessly"

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