Its been a long time since I rebuilt one, but I think you determine the wear on the gearbox based on the preload torque when you cycle the rack thru its whole rotation.

As long as the teeth are worn evenly, you should be able to revive the box.

But then again, that box has seen better days... So your guess would be as good as mine, I don't remember seeing any bore tolerance specs in the book.

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Just my MB's:
1990 420sel - Winter DD - 410,000km
1990 560sel - absolutely showroom mint - 360,000km!