I bought a new belt with the attached link and tried this fix, but due to an unexpected problem it hasn't worked and I fear I may have caused further damage (see my comment above). Any advice would be welcome please. Thank you.

I got to this stage very easily, but I couldn't get the grey plastic cover to slide out without a great deal of force. When it did move it was very stiff and made a loud clicking noise, as if it was turning a gear wheel or ratchet or something. The old belt was well stretched and I managed to fit the new one, and then I had the same problem forcing the cover back in again. Unfortunately this hasn't fixed the problem and the tray still doesn't come out when I press the Open button and I am worried that I may have caused additional damage by forcing the cover out. Any advice would be welcome please. Thank you. Peter.