Nate: If you are the least bit handy with a screw driver and needle nose pliers, then you can repair your old ones.
The problem with the eye ball vents, at least on my 1966 pa-30 is the rubber tube inside the vent that over time becomes brittle and cracks and eventually breaks.
You need to remove the vent from the plastic holder then remove the three screws on the back of the vent to allow you to remove the internals of the vent.
You will then see the rubber tube.which is tied to the vent apparatus on both side with thin wire and a little glue. Remove the wire and remove old rubber tube. Go to bicycle store and buy an inner tube size 700x20c. (this is the smallest diameter tube I could find)
Cut the tube to match the old rubber tube removed from the vent and install using a little instant glue to hold in place. Then using 20 guage brass wire or equivalent, wrap wire around both ends and twist tight.
Reinstall the tube back into vent and secure with the three screws and you are set for another 25 years!
PS if your vents are different than mine....disregard all above!
Happy cool flying!
Gary