Strange, looks like somebody's home made hack, HP didn't even bother to make a new bezel for the LCD.
Do the lines go all the way across? Looks to me like they don't, which implies that the problem may be in the system that creates the image rather than the display itself. Do these scopes have a VGA output on the back you could try with an external monitor? For intermittent faults like that one of my favorite techniques is to gently poke, prod and tap parts with an insulated stick and see if I can find something that reacts to my touch.