Cogwheel print and faded on left of Lexmark T640

[SalvadorFreeman]

Hello, after first trying a different toner cartridge and later a new one, I was still getting fading. So I cleaned the transfer roller. Now I am getting faded all down the left hand side of the page and a cogwheel impression down the left hand margin of the paper. Any ideas anyone? Thanks.

 

[SalvadorFreeman]

Fixed it, so I'll post the solution in case it helps anyone else. It turned out that the transfer roller had been put in the wrong way round!