looks like the contacts on one side are starting to go. Does it show all lines when you apply soft pressure to the edge of the display or the case?
The contacts shouldn't be an issue on the Game Gear, given that it's just a rubber strip on the screen. Unless someone's been messing around, it shouldn't be an issue. Looks like a screen problem - has it been dropped?
I don't know the history of the system or what's happened to it. It was on a site I was going to buy it from. Seeing that it's the screen it's self, I'd most likely pass on this.. Unless you can buy a screen from some where.
Ive not looked at a gear game personally - however I have repaired a number of phones and other things over the years. If it has a rubber strip as mentioned above that handles the connections from the PCB to the screen - they do wear out and break. I had to replace no end of them in phones around 99-2002 and they displayed similar looking symptoms to the ops picture.
I dont think the phones I used to repair would rot in 6 months. The screen had slight movement tho and likely moved while in someones pocket. But definitely not rot. 8210/8850 were 2 models I remember it happening to. Probably 5110 and 6110 too edit: link - http://www.bogpeople.com/nokia8210fix/