There are rebuilders of the heater valves. Here is one
http://www.heatercontrolvalve.com/ and there's probably more who advertise in the services section of Hemmings.
I don't know for a fact if the early valves use the same rubber piece as the 51 on valves but maybe someone on site does. If so and you want to attempt it, Napa sells the rebuild piece for later valves for about $12. When Kev rebuilt his he wrote up some excellent instructions and posted them in the how to section.
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