[Arran]

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  That style of pushbutton mechanism used little strips of canvas or some other fabric, which deteriorate with age and snap. I don't know why RCA used them when they used better mechanisms in other models of the same year, but they can be repaired I think. There was someone on the alternative forum who repaired a similar style pushbutton bank on a Stewart Warner using modern fabric if you want to go that route.
 What I find interesting about your T-55 is that there was a  Canadian RCA and a Canadian G.E model that was very similar to yours, but it had a shortwave band and a magic eye in the center of the dial backing plate. Obviously they used the same chassis design and just added the eye tube socket and the extra coils and bandswitch.
Regards
Arran