There was some kind of vaseline inside the scroll wheel covering almost all the holes in the scroll wheel's side. There is photo-transistor detecting those holes moving during the scrolling. I put paper towel under the scroll wheel and gave a good amount of WD40 into scroll wheel interior. Next morning the wheel was clean, all vaseline along with WD40 soaked into paper towel under the wheel. Assembled the mouse back and it's working nice. Update: after 4 months it's still working like the new thing.