[BrianG]

Any BEC currently on the market that I know of has the same basic circuit design. If the BEC fails, full battery voltage can be passed through it to the load. This is usually caused by an excessive voltage spike and/or high current loads. Since spikes are probably out of the question in this case, I would look at the servo being driven. I've had servos that appear normal on the bench have issues when running. In my case, one of the "axles" in the servo gear set had elongated an axle hole in the case. Under light load, it worked fine; under heavier running load, the added stress binded the gears. When that happens, it can pull a substantial amount of current.