I've just bought a class 50 and both ends had dislodged screens. I found prising out the light unit between the desk and the roof made is easy to po the desk out. Clipped the windscreen back in light unit back in next and then located the desk into the groove in the light unit and gently clip the desk forward to click into place,again take a bit of pressure off the sides to make it easier to pop bits in and out. No glue necessary but ths must be a common problem but at least it's an easy fix!