When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I don't have the answer to your question, but here's what I did: A lot of cotton swabs soaked in interior cleaner did the trick for me. Inside and outside of the circular vents, including the slats and flaps.
Never taken the vents out but the ring around the 2 vents in the center come off by twisting them (I believe) counter clockwise. Might be able to figure it out from there.
Dried coffee in /on mine from the previous owner(s) Should have seen what the cotton swabs looked like after a swipe or two. The carpets were worse. But I digress.....