Oil Leaking from Turbo??

I went under the car to investigate a suspension clunk when I noticed an oil leak. I traced it up to the turbo area. When I got out my mirror, it seemed that the leak was coming from the turbo itself. The turbo was dark and oily right where the compressor housing meets the turbine assembly. I thought the turbos were supposed to be air tight, how could they leak oil? Is there another place it can come from?

I'll be honest, I didn't get the best look at it, I was using a mirror as my endoscope camera turned out to be another cheap POS dud. Anyway, has anyone had a problem like this or can recommend where to look?

Thanks!

Oil Leaking from Turbo??