Metric Mechanic rebuilds trannyies (the car parts that is... not the sexually misguided) so you may want to give them a call and see if they can't send you a fixed one for your core.
I have a couple 1990 535i manual transmissions because I'm always afraid I won't find them. I'm going to get the one of the shelf checked out and get all the seals replaced for sure if everything else checks out fine (play in the gears, sprocket wear, etc.)