In replacing the center vent actuator diaphragm, I cut away as much as I could of the existing diaphragm and used the kind of replacement diaphragm designed for the second chamber of a dual chamber actuator (one has a slot, one doesn't).

The recirc actuators behind the glove box and all except the center vent actuator use a bayonet mount. Take note of how they're installed and pull them out to service on a bench. dual chamber actuators have an intermediate position between full open and full closed. The recirc actuators work in parallel. Pulling a vacuum on the outer chambers pulls the flaps to about 85% closed. pulling a vacuum on the inner chambers pulls the flaps to about 15% closed. Pulling a vacuum on both chambers closes the flaps all the way. Or something like that.

Sixto
95 S420
87 300SDL