Punky, Larry Stock in NV rebuilds all the calipers and has the kits and some plastic parts available. (www.panteraparts.com)
I think they're nylon which hardens & gets brittle over multiple decades. Note that there are many metal parts on these calipers that interchange side-to-side, and which defines which side the assembly fits on. It's an easy mistake to swap parts side-to-side and wind up with an assembly that cannot be used on your Pantera. I've done this. Take lots of photos before ripping yours apart. Note that the Pantera Service Highlights manual shows a rudimentary rebuild of the calipers.
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