L322 (2009) Rear wiper issue.

After strip down and Refurb (new nylon cog wheel, New seal ring & regrease) of rear wiper motor, after reassembly, the rear wiper makes 4 sweeps as soon as the ignition is switched on but functions normally from the stalk switch after that. Additionally rear wiper does not park properly.
I never understood the function of the magnet on the underside of the new nylon cog wheel (the news one was a slightly different configuration to the original) so thinking it might be to do with that and/or the relay box fitted on top of the motor.
Rear washer which was working before the Refurb has now also stopped working.
Appreciate any help on this.

You may need to pull it out and go back over it.
The chances are the magnet is a position marker for the motor. Get your tools out

Mark Piercy said:

You may need to pull it out and go back over it.
The chances are the magnet is a position marker for the motor. Get your tools out

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As Mark stated, the magnet will be the park position sensor, probably operates a reed switch or such like.