My 3GS is 7 years old now, and I find that despite pressing the L or R to turn on the green LED, after stopping and restarting the engine, on reverse, my auto dipping wing mirrors keep losing the L/R green memory, so they will NO longer auto dip on reverse, unless I open the hidden control box above the driver's left knee cap, and press either the L or R button.

Is this normal?
Any simple way to repair?

 

Are you getting any skipping crunching sound of gear when they move? You may have gear that chipped or worn over time. Try un bolting the battery for an hour and plug it back it see if it comes back. Your sunroof, mirrors and windows will all have to relearn them selves so maybe that may fix it.

If all else fails, see the left and right button on the drop down, if you carefully press in between it turns off the auto drop and basically they become manually fixed.

 

I brought the car into Lexus, and I found out that when the 12 volt lead acid battery is low in voltage, the car NO longer remembers the left or right position, hence restarting the engine, the wing mirrors have lost that LHS/RHS memory, hence the reverse auto dipping wing mirror feature no longer works.
A brand new lead acid battery instantly solved the problem!!!

 

Another interesting observation.
As the OEM battery gets older and flatter, the old 3GS has more difficulties with engine starting a struggle, and the vehicle auto central locking at speed NO longer works.
It's all to do with the voltage of the battery getting old and low.