Thanks to soakinader, you were right and I was able to open the 1500.
I have performed the rubber band repair and fixed the firing valve, however I have a new issue. The blaster does not hold pressure, and leaks like crazy whenever it is pumped. I opened the PC expecting to find a ruptured bladder, but the bladder is perfectly fine. Is this an issue with how I reassembled the blaster, or the maybe the piping? Or is the PC still possibly ruptured, but the hole is so small that one cannot even see it when it is not pressurized?
UPDATE: I submerged the 1500 is a tub full of water and pumped it. All of the bubbles came from the area by the firing pin where the rubber band repair was performed, so I guess I have to open up the firing valve now.
ANOTHER UPDATE: I removed all of the screws from the 1500's firing valve, but I cannot separate the two halves. Am I missing out on something here?
YET ANOTHER UPDATE: Never mind, I pried the firing valve open and the seals were... perfectly intact. Is this a misalignment problem?