An update on my progress.
Originally I found rust in the hinges of both my front seats. Taken in, first they'd seen of it, and cleaned (rather than replaced as originally advised).
I then found rust on the lugs that hold in the rear seat centre fold down, so I contacted my dealer. After that, I then found some rust under the front seats as well. The car went in yesterday.
I was fairly clear in my discussions with the dealer that I had no confidence that rust won't reoccur - especially if I can find rust in seat parts (that I can see) AFTER they make an initial fix.
Latest response from the dealer today by phone is that a "repair kit" is being issued by BMW Australia later this month.
Does anyone else know any details on the "repair kit" ?
Once I found out more I'll advise.