ABS light keeps going on

Hi guys,

I have a problem with my Aveo. ABS light sometimes pops up. After months of troubleshooting, I've figured out how it happens:

When I start braking (no matter how lightly I press the pedal and no matter how slow I go) sometimes the brake pedal will act up and start shaking lightly and there will be a scratching sound coming out from the front wheels, similar to what usually happened a few times when I had to violently brake to save myself (ABS kicked in).

After this mini-event, ABS light pops up after ~10 seconds, and my ABS does not work anymore, but the car brakes completely normally (but without ABS, so wheels will block if I press hard enough, so it's basically old-school way of braking).

I've googled that it may be due to the "wet" braking oil. We've checked that my oil was in fact never changed in like 60k kilometeres and that a testing pen shows that it's wet. We've changed the oil and that made the error stop appearing for a month.

And now it's back.

We've checked the braking pads and discs, everything looks OK and has been changed way less than 10k kilometers ago.

What remains? ABS sensor? Should I just assume it needs to be cleaned up, because it wrongly thinks that it must employ the ABS when it doesn't? Or maybe it's just ****ing dead?