I searched all around the statues but I wasn't able to find the "Device" in sector O3, so I completed the game by forcing my way into D's Palace, then the basement. I reloaded a pre-victory saved game and fought my way into the O3 sewers and was able to find the ladder up to the surface level. Still can't find the device that opens the statue that lets you back down.

The remote control is inside the small building at the bottom left of the maze. I've personally had at least one game where I couldn't find it either, but I can't confirm or deny that it's the same case.

It should be in the main building. Probably either on the glass table or in a cupboard. To use it you have to stand on very specific tiles in the main building (try the carpet ).
If everything fails, you can always blow up the statue...

Fidel's way of solving everything worked fine! As with refuelling trucks, etc., had to walk away to get the movement icon. Then it dropped me in the sewer water (not by the ladder) .