On my D the car starter motor stopped working all of a sudden. Typically this was after I had just overhauled my auto circuit board.
I took the starter motor off. The solenoid operated but the starter wouldn't spin.
I put the starter motor in a vice.
I used a jump start pack black lead on start motor casing and briefly touched the lower terminal with the jump start pack red lead. This spun the motor. Cause was a duff solenoid ie the copper strip had burnt out.
Why not try this, the solenoids are a weak point.