Cleaning contact with rubber on door cards

[notorious]

Hello guys,

My 2002 A8 has light grey color leather door cards that are contaminated at the line of contact with rubber "gasket" arond the door.

I bought the car with this contamination problem and now i'd i'm trying to clean it. I tired leather cleaning stuff from Autoglum, but it doesn't work.

Any suggestion how to clean those contact lines???

See the picture below. I'm talking about dirty line that goes from the upper right corner of the picture.