Hi
There was should be overheating causing the head of laser tube separated
Maybe sometimes you use the laser to works but forgot to turn the water cycle on.
I suggest you should be buy a new one to replace.
If you glued it back by some adhesive. i think the laser tube should be broken,
At the same time, there may be leaking when you turn the water pump on.

Sincerely
Tom
Thunderlaser- leading provider of laser cutter and laser engraver from China