[EC900]

The gears may just be dirty or gummed up from non-use. When I bought a R side mirror to aid view, I was able to bench test the motors for operation with a 12v tool battery before assembly, seemed stiff but maybe that’s the way it operates. I never bothered to re-wire (no harness). Did you open up the unit to get a look inside?
Manual adjustment w/o using the motors, the mirror glass was stiff enough to withstand door slams. Good enough to set and forget.