The vent direction is maintained by two pieces of felt material about 3/4 by 3/16 placed on each end of the vent. Easy enough to find at a hardware store. I imagine the round felt stickers for coasters etc would work.
There are two tabs, one on each end that hold it in place. A thin blade screwdriver can be used to pull them in, but just enough to move the vent pin out of alignment with the hole. These things break off easily and I haven't been able to find a glue to hold them in and still be able to clip them back in place.
DAve