fuser unit is broken hence the line, it can't fuse the ink onto the page in that area where the line appears, or the drum is goosed. one of those, no matter how much time you spend on it they can't be fixed and aren't worth trying.
i assume you mean the green drum? they are not to be exposed to area light as the drum is the whole reason laser printers work at all. it's a photosensitive drum that changes polarity in small areas ie miniscule dots resulting in text that are then fused to the paper with heat at 200 deg.
The problem is the parts you need to replace are expencive the fuser if it is broken are around £80, it would appear that each of the toners has it's own drum so replacing the whole set may or may not resolve the line issue.
either way it's about cost now, do you get a new printer or repair that one at a price, if you repair it could fail again meaning wasted money.
Getting a new printer is the better option as you may still have intermitent feed issues that really aren't worth dealing with.