Kyocera FS 1750

I have a cleaning problem.
After changing a toner cartridge the printer has started to print a grey
band about 25mm wide down one side of the page.
I have cleaned as instructions that came with cartridge which improves the
prints about 50% for about 50 copies and the it gets bad again.
The printer has made about 50K prints from new and worked great up until the
last toner change.
Anyone any ideas
Thanks
Bill