A Rohloff's a damned expensive gearbox. I take the view that, even if you know that 25ml of oil is overkill, a service kit and delivery is only about thirty euro (and much less you buy in bulk and so save on the delivery), well worth it for the peace of mind. As for the mess when the excess oil comes out, as it will, well, it happens on one or two days (and for no obvious reason), you wipe it off the hall tiles or let it soak into the shed floor, and then you're good for another year. If you happen to be touring Tassie when it happens, count yourself lucky!
As for worrying, I wouldn't. What I would do though, is at the end of the tour to sacrifice a service kit to run the cleaning oil through it to get the gunge of the tour out and put clean oil in there, rather than let the box go for x months more, commuting or incidental riding or whatever, until the routine annual service comes round again. That seems a reasonable precaution to me.
Andre Jute