Mine has recently stopped leaking oil, but been marking its territory on my bike shed floor regularly which I later also identified as coming through the gear shift cabling area which is now 'well lubed' on the hub side. I had wondered if it were through the quick release, but after drying all with a rag and checking daily, the gear area seems to oil-up before the QR gets wet. My bike was purchased second hand a year ago, and where I did an oil change a month after purchase, which is when I first began to notice.
Initially I could not see where the drops were coming from, and put some masking tape over the oil change plug to see if that was the source. This proved to stay dry, and the drops continued to appear overnight but only if I had ridden the bike. If it had been standing, the drips either stopped or were less noticeable.
Having trawled the net for myself, I found several English and German sources saying that drips are not unusual not a huge concern and could be from the 'overfill' from the recommended oil change and partially due to air locks that might have got in when draining and refilling. As the hub can run 'dry' for up to 5000km I am not too concerned. It recently stopped dripping, and I will do the 5000km 1 year oil change in 2 weeks- and plan to change the paper seals on the internal gear element along with cabling when I do so. I am hoping I can establish if the seal is the source of the leak. The seals themselves come with the gear cable kit but can also be purchased seperately. What I can say is that my hub is running more smoothly than when I purchased the bike a year ago- and does not seem to have suffered as a result. When I drain the old oil in a couple of weeks, I'll try to estimate how much is remaining. I'd used one of the one time flush and oil kits on the change last year, so have a pretty good idea of how much went in initially.
Until I actually do the change, I cannot confirm 100% my theory of my oil 'leak' source- but it does seem to match other on subject posts I have found. I'll be a little wiser by mid November after a few km following my servicing.