Welcome aboard !
Over the years, I`ve seen more than a dozen similar cases where the cause of the problem was a coin or two which had slipped down into the shift linkage, jamming things up. Remove the shift boot, and inspect closely with a flashlight.
Your car is an E34, so any future questions should be directed to the E34 Forum.
The road goes ever onward....
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When faced with choosing between two evils, always go with the one you`ve never tried before....