Vacuum pot/actuator/canister for HVAC doors

The vacuum pot that actuates the air-recirculating door on my '72 Dodge truck is going out (has a hard time returning the door to closed position), anyone know where to find a replacement? Or if there is a way to "repair" it? I'm guessing the diaphragm inside has a small tear or leak of some sort. Or does the rubber grommet the rod passes through also act as a vacuum seal for that side? I might try putting some grease on the rod and see if that frees it up but I've tried to find these vacuum pots before and never had any luck. It is the dual-acting type with a vacuum line going to each side.

I think my '70 Duster needs one too now that I think about it, pretty sure the one that switches from dash vents to windshield/floor vents is "sticky" too. Have to reach under the dash and manually move the rod.