It might be Robby Robbins you're referring to who played keys for him (Seger).
It also might be a chamberlin and not a mellotron as well.
According to the person I purchased my chamberlin from, the chamberlin belonged to a fellow named Tom Neme (receipts for repairs are abundant!) who had purchased it from Robby Robbins (Seger's keyboard player).
Although he was sure it was used professionally, he didn't know what recordings it was used on, so the only way to ascertain this is scrutiny of liner notes. I believe it's possible since everyone involved was and is local to the area, but apart from said receipts there is no paperwork to back it up. Perhaps some phone calls would yield some info.
Turn The Page does sound more like mellotron than chamberlin to my ears though.
Chris
Thanks for confirming what I always figured about the Seger. Who played keyboards for him at the time? I don't own any Seger, though this is such a great song, I wouldn't mind having a copy!