The inaccuracies of draining the oil to measure how much you lost is likely not worth the effort, especially at the price of Rohloff oil. And if you got a number, you have nothing to compare that number to so would that number actually mean anything?
All Rohloffs are expected to slowly lose oil, but I am rapidly concluding that the difference from one hub to the next is how fast that slow loss is. Mine appears to be more rapid than most and I plan to check some gaskets later, but it is 3.5 years old right now and I am not going to worry about it. Most of my oil loss is on the left side, so I know where to start looking.
This recent thread had a lot of discussion on oil leakage.
http://thorncyclesforum.co.uk/index.php?topic=11971.0I think that the current Thorn recommendation is to put in 15 ml when changing oil, not 25. I do not know what you put in. Putting more in means more will leak out.
One thing you might want to look at, if you were actually getting noticeable drops forming during your ride, that suggests to me that you are losing it pretty fast, is your drain screw still in the hub or did it fall out and cause the leak? I put a small piece of tape over my screw, although the tape probably does absolutely nothing.
Dave (from the SJS shop) pointed out in a previous thread that loctite on the screw is a good idea if you re-install the old screw to reduce the potential for dissimilar metal corrosion, besides making it less likely that the screw will fall out.