Auto dimming door mirror problem

Hi

I've fitted my car with a pair of auto dimming door mirrors, both driver side and passenger side, on my Octavia MkII FL. Recently the dimming of the passenger side works slower than driver side.

I've simulated the working condition by parked the car in a garage and turned on the interior reading light, then checked the voltage of both the door mirror. The driver side mirror was fine, with a voltage of about 1.1V when working, but the passenger side mirror has a 30% loss, with about 0.77V. But if I unplug the mirror and test the plug directly, it has 1.1V, which means the wiring was correct and there's something wrong with the mirror.

The photo demonstrates the voltage I tested. The mirror in the photo is not the same part on Octavia MkII FL but has the same mechanism. The plug I tested (as red line indicates in the photo) was from the car's wiring, not the one on the mirror.

Anyone knows how to solve the problem or if I have to replace the mirror?

Thanks!

Dylan