MJPerini wrote:
If you intend to replace it, try to find a newer similar part, because rubber & plastic deteriorate over time. Most old cameras used similar stuff and sir mirrors are of similar size. Keep the old one for reference. I would try to speak with some camera repair techs, because even if they don't have parts, they may be able to describe the best procedure.
Good luck
The cushions are available online, not expensive either, and seals too if one wants to do those.