Tapatalk is being removed immediately. There are security issues and there is no justification for having it anymore. I apolgize to those die-hard Tapatalk users but you'll need to start using the forums mobile version instead.
That's for the upholstery shop to fix. I expect a seat rail from the E3 (Bavaria) sedan will also work. Possibly from an E12 or even an E28. Production years of those run into the early 1980s, so they are getting hard to find. Someone on the list will likely pop up with one or more.
You have to tell us whether the missing rail is the inboard one (closer to the center of the car) or the outboard one (next to the door).
Hey Jahan - I have a set of seats I was arranging to move (Tom gave them away for free), but the really cheap shipping we had arranged fell through and the buyer doesn't seem to want to pay for alternative shipping.