John,
The heater in your photo is a 1953-1955 Fresh-Air/Air-flow heater, which differs from the earlier "deluxe" heater by having the cable-operated recirculating-air door on the front side. I think Lonnie mentioned these differences in a post that was lost (before we saw photos).
Just for correctness, the name Recirculating Heater refers to the less expensive GM heater that was used from 47-55. It had no Ranco valve.
The 53-55 cable controls the door, and the 47-52 cable controls the defroster flap. The defroster flap on your heater is controlled by a lever attached to the flap on the heater box.
Classic Parts will rebuild a Ranco valve for $50, but you need a rebuildable valve (as others have posted). You might have to resort to buying a new or rebuilt valve for more than $100.
As suggested above, check Bill's, Lonnie's and any other leads to a Ranco rebuilder, to see if they have a rebuildable core. Jim Carter might have one - also check BowTie Bits.
