Super Soaker Central

I'm trying to repair the firing valve of my old (old) CPS 3000, but it has been sealed shut with some sort of adhesive, and I can't get it open.





I've tried using a knife, but had no luck.
I've considered using a saw to et past the first of the stuff, but I'll hold off on that one.
Maybe I should sand it down a little?

Does anyone have any experience opening these things?
Any help and/or ideas are much appreciated.

Edit: Box cutter did the trick, looks like the adhesive was just along the seam, not in it.

I'm glad you found out the trick. Thanks for posting this for others to know in the future!

If anyone does end up doing this, just a reminder to use as short a setting as possible on the cutter.
It would be really easy to hit the rubber seal, and I don't think that it would be easy to replace.