Every year at the beginning of the spring and the winter there's a puddle of oil under my Rohloff. Since I do the oil change in the first week of January, and put in only 15ml of all-seasons oil as advised by Rohloff, after thoroughly draining out the cleaning oil, there is no question of an overfilled gearbox. In fact, after I instituted the 15ml routine, my gearbox has been pretty clean, whereas before it always had a trace, or sometimes a smear, of oil on it. The leakage has to do with the change of heating (the temperature in the space where the bike stands is controlled by the dial for the house temp) about that time, and possibly with the natural air pressure change also noticeable where I live at the change of seasons. Leakage is the wrong word though, as it is more of a misting of oil out of the breather vent in the axle. So I'm not surprised at all by George's tale of airplane journeys causing oil to mist out to the extent of a small puddle. You wouldn't even need the airplane journey, a truck hauling a bike to a different elevation would probably have the same effect.
These "misting" events I've observed don't last long, a couple of days or so, then the gearbox settles down as the internal pressure adjusts to the external pressure. It is not necessary to top up the gearbox even if appreciable amounts of oil have spilled out: enough clings to the gears to see you through to the bike's next oil change.
Note that some of the so-called "seals" on the Rohloff box are paper. A little oil mist on them probably aids sealing.
