[c02laser]

I have had my chinese laser machine for about 15months now and overall been pretty happy with it. I would say it gets used roughly for 3hrs a day 5 times a week. Judging by that i work that out to be some what 900hrs of tube use. A few days ago i switched the machine on and went ahead with some engraving, it started to make a loud ticking noise which i couldn't figure out where it was coming from. I left it to carry on so i could locate the noise, and found it to be coming from the laser tubes access door. I also saw flashes of light which i automatically assumed to be sparks so turned of the machine to further investigate. Got everything unpluged and lifted the rear hatch and noticed black burn marks on the casing where it must of been arcing. It had seemed as though the rubber seal had detoriated and caused the power lines to spark onto the case. So i did a bit of research on what kind of seal this may be, the closest i found was a "silicone compound to reduce the chance of high voltage breakdowns".
If this is the silicone that was used then why did it break down? How can i avoid it happening again? Is there a better method of attachment or quality compound that can be used.
I contacted the supplier and showed him the pictures and his response was "your tube seems to be damaged causing the arc" is this true? Is there anything that i could of done to prevent this?
Thanks