If you have a spare toner, you can try that. Sometimes the extended life cartridges will fail a little earlier than expected, but generally you'll see toner just on the edges of the paper- not making a shadow.
I'm almost 99% certain this is going to be the fuser wearing out on this machine. After so many years, bearings can wear out or the fuser films just become so degraded or contaminated that they just wont fuse properly anymore. The heating elements can also get weaker, and that's probably why your seeing that shadow- as the paper goes through the fuser, not all of the toner will adhere to the paper and some will stay on the fuser- giving that shadow effect.
Probably more cost effective to just replace the printer with something like a M402.
I am not a HP employee. I am a service tech on these forums researching topics and offering my best guess to aide in your troubleshooting.
This topic has been archived. Information and links in this thread may no longer be available or relevant. If you have a question create a new topic by clicking here and select the appropriate board.