don't worry about the oil. Look at some Boxxers and Dorado's, they are renowned for having oil rings. All it is the fork has an Open Bath oil system as mentioned above. This means that the way it is setup also allows for a little bit of oil to lubricate the stanction and seals, this will allow a little bit to come through and voila... little black rings of oil and dirt.
As for lubing your stanctions, there are some lubes specifically for that, one that my friend uses on his Dorado's is called Fork Honey, it is thicker than lubricants like Tri-flow and doesn't flow down the lowers, or in your case rim. As your fork is inverted, I would recommend not using a free flowing lube on your forks as it is quite possible it would flow down/splash on to your disc rotor. For that reason, try to find a specific fork lube like the mentioned Fork Honey.