Chattering regulators may possibly be only the deformation of the base material backing plate. My various 123's had several, all of which are now aligned, cleaned, lubed and back in service.

Remove the suspect regulator from the vehicle and check for obvious tooth and gear damage. Then check alignment.

I did pics in a post on how-to.

Good luck.

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FRANKNBENZ

1985 300D "Old Blue" 265,000 (parts car )
1985 300D "Gray Ghost" 245,000
1985 300D "Silver Bullet" 160,000
1975 914 VW/Porsche "BC Car" 125,000
2010 Prius "Shocking!" 60,000
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