I'm a mechanical engineer and design high performance military avionics. I know from experiance that sometimes what looks the worst is not what caused the failure. Having said that, I must say that I would first suspect any plastic parts of the system. From time to time we've had had product failures in good, well designed parts due to plastic resin lot variations, a molder making changes in the additive package, the compounder changing the molecular weight distribution, or someone along the way not maintaining good control of moisture content in the resin. When plastic is good it can be great asset to a product, but controls need to be in place.:(