Original expansion valves were R-12. MB does not sell R-12 expansion valves anymore, I am not sure of the aftermarket suppliers. Its okay to use R-134a expansion valves with R-12 its just that the R-134a parts flow more. You may very well have R-12 in that system if the original fittings are still on the car. There are testers that can determine what kind of refrigerant you have, but I don't have much info about them.

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Brian Toscano