LaserJet 2420 grey background

LaserJet 2420 grey background
Here's part of a page printed below.

Most of the left side of the page has a greyish irregular background, maybe 10% grey. The text is a bit faded and sometimes broken up.
I got this printer a few months ago, Has 207,000 pages on the clock.
I had another printer, same model, that was having a lot of jamming issues, so I took its 90% full toner cart for this and it printed perfectly.
The fold out "tray 1" was damaged though, so I took the tray from the other printer. To do that I had to take off several panels and take the toner cart out. I did try to protect it. Cleaned dust out of the printer while I was at it. The print seemed to be still OK, then. I disposed of the old printer (no room for it.) But shortly after this grey vertical bands appeared. I made a couple of the cleaning pages and ran the clean cycle, but made no obvious improvement.
Is this some damage I did to the toner cart when doing the repair & clean? Can it be fixed, or will a new cart fix this?

https://i.imgur.com/ITyEaeX.png

Don't know if you got it fixed yet.
If you haven't....from the manual:-

Gray background 1. Do not use media that has already been run through the printer.2. Try using a different type of media.3. Print a few more pages to see if the problem corrects itself.4. Turn over the stack of media in the tray. Also, try rotating the stack 180°.5. Open the Configure Device menu at the printer control panel. On the Print Quality submenu,increase the TONER DENSITY setting. See the user guide.6. Make sure that the environmental specifications for the printer are being met. (See Operatingenvironment on page 9.)7. Replace the print cartridge.8. The power supply might be defective. Replace the power supply.

The toner cartridge is not that fragile.

Also the transfer roller may need replacing.

Just some thoughts