On my 1999 ML320 the passenger side dash vent control wheel is stuck in the closed position. The open/close wheel does not turn. This is the single vent over the cup holder. Can anyone advise me on how to fix? I presume I need to pry out the vent unit but before I started messing around I'd like to know what I am doing and this forum is the perfect place to get help. Thank you in advance! Rick