Very Similar Problem
I spent 20 years as a computer trainer. I was sent out to do software training for a company where everybody had their own laptops with built-in trackballs. (LONG ago.) One user could make the cursor move up and down, but not side-to-side. Classic dirty mouse symptoms. So I turned the retaining ring, popped out the trackball, and looked in. This model laptop was light gray plastic, but hers was orange, and gritty.
I asked her "What have you been eating?". She held up her (orange) fingers and said "Cheetos". It took about 15 minutes to scrape the Cheeto-dust off the rollers in that trackball well. .