Smudges when printing from Dell 1235cn

Hello

I have had a Dell 1235cn all in 1 printer for about 10 years now, and during that time it has put in a sterling service. Unforutnately over the last few months I have had problems with smudges of yellow and black toner appearing on my printouts. This happens if it is colour, or black and white. After a certain number of prints I get a clean page, then it starts happening again. I have attached a picture of an example printout.

Can someone please advise me on what to do to resolve this problem. I would rather fix this issue and not dispose of an otherwise good printer, especially as the toner cartridges are nearly full.

Thanks

Andrew