i'd suggest a search about the cowl vent seal, and it's installation, there are several threads and discussions on this site about it.
no cable or other connection to the dash, it is operated by the under-dash handle.
unless you really do mean the fresh air vent, which is used for the under-dash heater, and is located on the passenger side of the firewall. this IS cable operated, and goes to a knob on the dash - it would be an optional console added to the bottom of the dash. there is no handle associated with it, though, which is why i assume you really mean the cowl vent (especially since you mention the difficult to reach screws and rubber).
good luck with the wiper pivots, probably not easy to find.