I'm the other poster PH refers to.
If you have the EXT black cable box and you undo the big stainless knurled screw, and pull the box off the pins guiding the fit, you hold in your hand a black box closed on all sides, and with your right forefinger you can point at a newly exposed brass nut on the bike which is driven by a female socket on the other part in your left hand to change gears. If you have an 8mm socket or open spanner in your touring tools, in case of cable breakage, by rotating the brass nut with the spanner you can change the gears to some compromise that will at least get you to the next habitation.
The shaft behind the brass nut is clearly connected to the gubbins of the gearbox, and it seems to me logical that oil might try to get out that way. It hasn't ever on my bike that I can remember. I pack this space with Phil's, a tube of which was given to me by the erstwhile Forum member Jags a few years ago with assistance from Dan to orchestrate the American end of the long chain from California to the wilds of West Cork. I'll return to this in a moment.
About the piece you're holding in your left hand, still attached to the bike by the cables: on it is the female part of the gear changing mechanism, looking like the female end of a socket spanner. Behind that, inside the box, out of sight, is the cable drum and the mechanism to turn the pull-pull action of the cables through a right angle to drive the socket and hence the gear change. I took one look at the schematics, considered for the space of a cup of coffee that I'm a notorious fumblefingers, and decided not to open mine except a sliver to peek inside for signs of corrosion. My bike lives an easy life almost 100% on tarmac, is never ridden through water over hub height (if I need to jump off the bike into the ditch/stream in the harvest season to clear a narrow lane for a big agricultural machine, I hold the bike above my head) and I wasn't surprised to see no evidence of water ingress. I'm not planning on opening that box -- for clarity, the half where the gear change cables enter it -- until I replace the cables, which have lasted an enormously long time when one considers that they live under abnormal tension because I have the handlebars so high. I should perhaps add that most of you are nearer to SJS by a factor of ten or so than I am to Rohloff itself in Germany, so that is another factor I consider in not taking apart a component I may not get together again. (Yes, I'm aware that SJS sells rewound cables for touring spares and will probably make up a complete black box for me with cables of the right length attached, which for me would be a justified expense, probably a bargain for avoided frustration and lost rides with consequent health effects.)
Dan has also made the point on a previous occasion that one should take the part attached to the cables apart and grease the threads of the screws to avoid the whole thing being locked by corrosion between dissimilar metals.
As I say, I pack the bikeside hollow with the brass nut in it with very high quality grease, enough to squeeze out enough on reassembly to cover the mating area of the two black halves of the EXT box, by the test of grease squeezing out around the circumference of the box. Oil not only hasn't leaked from there, it is very unlikely that it ever will. There's a breathing hole in the centre of the axle, and if that is a source of oil that leaks out, presumably it would leak to both side, but the grease stops any leak to the non-drive side. Of course this is pure speculation, but that space, with the two pieces of brass working against each other every time you change gear, is so easy to service, it takes more time to lay out the tools (one large flat screwdriver for the knurled nut, optional, one tube of grease...) than to clean out the old grease thoroughly and squirt in new grease.
There's another point. Whatever the recommended service to the EXT box is, one half or both, a lot of Rohloff owners don't even know they're supposed to service it, and we've never heard any huge surge of complaints about failures. It seems to me that Rohloff, which generally suffers from a case of cover-my-arse on the extreme end of the scale even for German engineers, have outdone themselves by the instruction to service the EXT (whichever parts of it they intend) every 500 miles or kilometres or whatever. I did at first, until I started to think about it, and then tested alternatives, and now I do it every 3000m/5000km or one year when the gearbox oil is changed. And still I've never seen the slightest evidence that changing the grease was at all necessary, zero ingress of water, zero egress of oil. Those of you who do much higher mileages than me, or whose bike is used in extreme conditions may have different experience and hence service schedules, but for most utility bikes and bikes used for short tours in civilisation, that service instruction in its over-the-topness exceeds even the possible damage by the confusion of parts of the EXT box in the service instructions.
Of course, if you use your Rohloff as a mud bike and spray it down with a pressure hose once a week, you should follow the service instructions closely. Also, if you're a newbie, follow the Rohloff book closely until you have the experience and the confidence to take responsibility for deviating. Notice how carefully Andy Blance reasoned out his deviations from the Rohloff manual.
A Rohloff HGB lasts a very long time -- nobody knows how long! -- and experience has taught that even the worst never-minds rarely find a way to damage it, so you are never in any hurry to make decisions about your bike's gearbox.
