Yep Corroded about 4" from the drum on off side (uk). It also looked as if some "rusting" had occurred after the break. Conjecture but it is possible that it broke a seized a while ago meaning the h/brake was only working on the near side where the tie wrap had broken.
Anyway all done & working. About 6 hours labour. Seat runner is now a bit stiff so more fettling to come.
