An update: It appears the actual case is fine, as when I swapped my new caseback and non-shrunk gasket onto the old case, the weight swung freely.
This was also useful as it appears there was some corrosion on my new model where the caseback met the gasket, but did not intrude into the movement. I guess I'll be ordering two gaskets and possibly two casebacks for both watches. I'm excited to know that the older watch wont need to be completely re-cased.
Also WUS seems to have a minimum post policy for pictures and links so I couldn't ask for help on the appropriate thread. My post also needed to be checked by a moderator before going live.