When you open panel 1 at the back of the printer their is small tray that has a spongy lift out roller in it, it is the only spongy roller in the printer as far as I am aware, all the others are hard rollers. I have tried cleaning this roller with both a brush and a damp cloth but as soon as I print anything yellow toner is getting onto this roller, only in the centre of it, and then of course onto the paper.
No the toner isn't leaking and yes you're right the doors are at the sides as per your image.
If the toner was leaking presumably it would be coming out of the bottom of the cartridge, which it isn't.
It's the door where your arrow is pointing to. When I shook the toner a little did come out of the bottom.