Here is why you moved the arm to the center position.

The part labeled 'indentation for gear' will only allow the small gear to be inserted at this point. This presumably will prevent misalignment at this junction. Insure on reassembly that the reciprical arm is in the fully retracted position.

The five holes marked 'cover screws' are what need to be removed to access the reciprocal mechanisim. Do not disturb the four larger screws, they hold the reciprocal guides.

The picture (#3) you are viewing show mating surfaces. i.e. the shaft pointing up on the right part gets turned over and fits into the hole of the piece on the left. Installed in the car, the part on the left faces the sky and the part on the right faces the ground.
Similarly, the gear on the right piece fits the half-round pinion on the part on the left. This gear and pinion should probably be lubricated. Would not hurt to hit the shaft also. I plan to use white lithium unless I hear a better suggestion.

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