Problem with gear of Toshiba e-studio45

Question

Good Day!

The copy of the machine has been alright but occasionally the page darkens but we just clean the screen and corona wire near the drum because it darkens. Do you think there is a problem in these parts.

The small gear (21 teeth) easily worn-out. I have just replaced it last june and it has been worn-out already in a month time. Does the gear easily worn-out or there may be a problem that causes it to worn-out easily.

Thanks again!