I would definitely seal the whole thing. The particle board just breaks down over time. I ended up with an entire side that I had to gently heat and work. So far is seems to be staying put, but I am sealing the other side.
When I bought this game it had been worked on. NOS monitor and boards are clean. My only issue is with the connection between boards. After a few minutes of play, the screen wigs out. If I move the boards a little it straightens out. I am assuming flaky connection between the two boards is the problem, but I haven't monitored voltages to see if the power supply could be the issue. The gun is in great shape except for two galvanized self taping screws used to screw the front of the crossbow on. You really would never noticed with it mounted, but I just can't put it back together without fixing it.