Bill, there was a change in the brake lines to a bigger size. My 1955 is a late one, and it has the big lines. Early ones were smaller, I'm not sure where the change took place.

With that, I'd agree that it is odd that it is only the right side, if it was a line problem, it seems like both would do it. But they must have gone to larger lines for a reason too. I've never had a brake valve stick like you are describing. I've had them leak, and get soft until they charge up and then work. Putting new seals in the brake valve takes care of all that.

That brake valve is in the dash, so it is going to be fun to get to. Could it be some linkage hanging up in the dash? 

I'm not sure if I was any help....