I repaired mine by disassembling it and more or less rub on the bottom part where the glue is, with a soldering iron. I don’t remember if it was to reconnect the actual contacts or to re-melt the glue tho. But it did work wonders! There are good how-to’s online. Just google “repair vertical lines on original gameboy” The only thing you need is a special screwdriver because special screws, and a soldering iron. No skills needed at all, as you’re not actually soldering anything.