I had an issue like this where the copies were coming out blurry on an hp 4350 and I have seen similar issues on an hp 4250. This is invariably a fuser issue and in extreme cases a swing plate assembly needs to be replaced. Don’t skimp and take out only the black gear on the swing plate assembly. Take out the whole thing. There is nothing worse than having to go back to a customer site and having disassemble a machine a second time just to get the white gear from the swing plate assembly installed.