Ok, so we've completely ruled out voltage as a factor and by the looks of it, it seems that it's only a relatively small percentage that has the faulty BEC components. As for the fan, well....
My fan actually stopped working yesterday, but I found a blade of grass blocking it. Removed the grass and that wonderful turbine noise returned.
Too bad the Muchmore fans I've been using on my MMs with zero failures are too tall to fit in the case. I may end up mounting them to the top of the case if the stock one fails.
My Monster has gone through about 5 full 4900mah 4s packs and is still running, so I'm pretty sure I got a good one. I'll be wiring up my second Monster (also from the first batch) tomorrow and trying it out so I'll be keeping my fingers crossed.