Not sure what might be causing that. I would remove the vent in its entirety and soak it in some type of cleaning solution such as Simple Green or Adams All Purpose Cleaner followed by a good rinse. You might also get in there with a detail brush or small toothbrush and work over the surface too.
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"The true delight is in the finding out, rather than in the knowing." - Isaac Asimov
'99 SLK230 Sport
'00 ML320
'95 BMW 525iA (RIP)
'99 Honda Passport
I have an 03 CLK 500 coupe that is doing the same thing and also the button that adjusts air mix and the two buttons that adjust the airflow on either side of the AC controls are so sticky its like they are melting. I have also seen this happen on C320 but I don't know what the cause or solution is.
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