[quote="xbacksideslider"]I'm not talking 961.
Just asking why a standard Commando's pin hole vent (the one in the fill cap) is inadequate, given that the rise and fall of temperature in the gear box is slow and that there is a good volume of free air above the gear lube as well.[/quote
If you are asking if the pinhole would work on a 961 like it does on a vintage bike, the answer is yes absolutely. It would relieve the pressure and prevent the pressure leaks. It however would not be Euro 4 compliant as you would be venting to open air. Some would say that it would let water in but it didn't back in the day!