I also wonder if the boxer engine design contributes to cylinder 4 failures at all. The downside of a boxer 4 engine from a balance perspective is that pistons don’t sit directly across from one another. The opposing pair of cylinders are slightly offset from each other along the crankshaft. This means they can create a torque that wants to rotate the engine about the vertical axis and create a rocking motion. This rotational moment could in theory accumulate at cylinder 4 and possibly cause deformation. The flat 6 design doesn't have this problem.