Chosen Solution
my MBP now has a horizontal green streak on the screen - any ideas what that means?
So we can tell the display its good. If the display its self was bad you would have also seen the line on the white screen or some color distortion on that location. What you are seeing is noise likely from corrosion on the connector on the logic board or the cable is slightly damaged so one of the lines is touching chassis (ground).
Your problem my friend is almost certainly a bad display panel. There are a couple of ways to tackle this problem but the most efficient and easiest fix for this is to go over to eBay and pick up a decent used display. You’ll find a good selection of them too. Plan on spending between $350 and $400 for the display assembly. The time to complete the swap will vary but you’ll probably spend about an hour if it’s your first time out.