I feel after all this talk of breathers that the original timed breather is designed to work off a very short length of pipe, be it steel or flexible, the longer the pipe the more resistance there is to exhaust properly. The original breather was short and exited to the ground (or the chain on a single) but this does tend to make a mess. When these bikes were new most all machinery dribbled oil on the ground to some extent, but this seems foreign these days, and in a world of mostly "Oil tight" machines. Certainly after atmospheric breathers became near extinct, the norm was to run a PCV system, where the circuit had some kind of high mounted vent pipe that draws clean air through the air cleaner into the engine, then the PCV valve mounted in an area where oil does not get flung at it, has a suction line plumbed to the vacuum side of the inlet manifold. So Martyn's idea looks good, and saves a mess........Though a crankcase vacuum system would be best, and this helps to minimize oil leaks as well. Don't forget too that on a standard engine, the cases also vent via the drive side main bearings through the generator housing in the top end of the primary. That's why if your primary oil level keeps rising after a couple of hundred miles, that oil will eventually get the better of the slinger mounted just inboard of the genny drive sprocket and leak past the generator. Some go to the trouble of sealing this area with sealant, but what are you really trying to achieve, the generator housing and end bearing wont stop the ingress of oil, which ends up all over the armature and commutator............
