The wafers in the tumbler is hanging up by gunk and not aligned by the key as it should. Spray penetrating oil in the tumbler to loosen up the gunk till you can turn the key. Get the tumbler out asap, replace or repair.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked