I have a 3 year old Brother laser printer (HL1112) which has behaved well until recently, until several marks appeared at regular 75mm intervals on every printout.
I discovered this excellent YouTube video which describes how to solve the problem:
https://www.youtube.com/watch?v=jivwdB-1zaY
I am sure that a similar procedure can be used successfully with other laser printers.
I took a torch to investigate the state of my roller and sure enough,...