The dealer does have it with the correct color code, but it may be hard to get them to admit they have it. The line you are talking about sound like the line that goeas to a valve on the front of the left fender that is used to control purging of the charcoal canister. I belive MB calles it the regeneration valve. If this is the line then you will need 1 meter of A 001 158 01 35.

John Roncallo