I wonder if oil leaks in diesels are caused by positive crankcase pressure. I believe this is a significant difference from ignition engines, which use manifold vacuum to suck out blow-by gasses. Diesels have no such vacuum and therefore blow-by gasses may find their way out every crevice possible, not only out the vent tube. Oil helps seal around gaskets and the positive pressure slowly pushes the oil out. This would be why oil can be found around the filler cap, vent tube, valve cover gasket, etc. So if a suction of some sort where placed on the vent tube (perhaps a small electric fan) might the leaking and mess be significantly reduced?