I used to have a redwood deck refinishing business years ago and I can assure you the best way to clean those louvered vents is to do what trident said and spray oxalic acid over the entire door...then take a household pressure washer with a 25 degree tip and CAREFULLY go over the door and vents. Always go with the grain when using a power washer. After everything dries give it a light sanding and treat with what ever you choose. We just re did the teak door on our Tsunami and it came out great.
I've heard people say that the power washer will remove the natural oils from the teak...that's a bunch of BS. It will not remove anymore of the natural oils then when you scrub and clean by hand.
strick