Transmission problems maybe?

I was under my car the other day and noticed some black grease substance above the connection point between the transmission and the drive shaft, what could this be?  Is the transmission fluid this color and texture?  Or is there grese in the drive shaft?  I have read about all the tranny problems and how there isn't much fluid in them so I thought I would ask.  I plan on wipping it off and rechecking in a few days to see if I can tell where it is coming from.  Any other ideas

I have an o2 Xtype 3.0

The grease cap is leaking on the propshaft. I needs replaced.

Thanks.  Do you know if it is a dealer part?  I'll be checking around.

I went by the dealer and he gave me a gasket.  Is this right?  It is circular so it means I will need to disconnect the drive shaft to put it on, that sucks.  Any good tips for doing this?  Any recommended grease, they just said us CV joint grease.