What's wrong with this circuit board?

I have had a recurring problem with the Circle Pad, and it all now leads to the circuit board inside its module.

When I move the analog stick downwards, even when pushing it all the way, the controls will never register a full-speed DOWN movement. When moving it in a full circle, instead it will make an oval-like shape. I tried calibrating it, but it always fails. Cleaning it with alcohol didn't fix it either, although I used ethyl alcohol.

There are visible scratches (don't know if they're scratches or corrosion) on the stripes where the slider contacts meet with the circuit board on the left side, yet only a small portion is actually affected.

What can I do about it without buying a replacement?