Help with Audi A6!

Audi A6 Turbo Diesel 1995 2.5 (stick)

119,924 miles

A few days ago I noticed our Audi leaking an almost blackish liquid under the middle(towards the front) of the car. Looked under the car and it seems like it’s dripping from the gear box. There is also a bit of clear liquid dripping as well but a bit further back…I’m guessing it’s the A/C doing this ?

Also, when the car starts there is a funny smell (like diesel) inside the car.

I also checked the oil and it’s black!( I know it needs to be changed.). I don’t know if this has anything to do with the problem or not.

Hope someone can shed some light on this problem.

Thanks in advance.