PROBLEM: Pump has broken off. (XP and CPS Plunger Style Pumps only)
CAUSE: Weak pumps + High forces. It's only a Plastic Stick. :P
SOLUTION: Dependant upon how clean the break is, or where on the shaft the break is, find a long, sturdy and narrow object that will fit cleanly into the hollow pump shaft.(Like a Pen) Stick the pen in the shaft and secure it tightly with a strong Epoxy Glue - be careful to follow the directions on the glue for mixing properly. When the glue is dry, the two halves should not wiggle independantly. (This Fix has been Tested - Works!)
(Credit for this goes out to Framling on Aquatica Yahoo Club)
-However, if the break isn't as clean (the shaft bent first before breaking, leaving mangled edges), trim up the edges or at least straghten them up with plyers before attemting the fix above.
-If the break is too close to the Handle or to the end tip of the pump inside, the above fix is not possible. If the break is close to the handle, then unscrew the handle off the broken part of the shaft, and drill new holes in the remainder of the shaft big enough for the screws for the handle to fit. Pumping strides will be shorter, but at least it'll work. If it is too close to the end tip to be repaired with the Pen method, nothing can be done. But sometimes there will be sufficient space inside the shaft at the end left behind for the fix to work. If the end of the pump shaft is lodged too deeply within the shaft of the gun, it may not be retrieveable.

PROBLEM: Does not hold pressure, leaks from inside the gun. (Not from out of the Nozzle)
CAUSE: Pressure Tank's Rubber Bladder Broken, Broken tubing or Cracked pump cylinder(the cylinder that the Pump strides in and out of).
SOLUTION: Assess the problem. Open the gun and examine the pressure tank. In Piston-Cylinder type blasters, you can see inside the pressure tank without opening the casing. See if there is a large rip in the pressure bladder (Meaning, does it look like a burst water balloon). If it does, it is too far gone.
-If that is not the problem, put a bit of water in the gun, pump, and identify where the leak is. Three places to check are the pump cylinder, the pressure tank, and the tubing between the internal structure. If it is the Pump Cylinder, pull the pump out all the way, tightly seal the crack with rubber cement(holding the crack with your fingers or vise-grips while it drys can help), and wrap it in Duct Tape or some other type of sealant tape. If it's the tubing, or any joints between gun and tubing, that is leaking, follow the same method of cement and tape as on the pump cylinder, but don't use as much glue. Remember when using tape to tightly wrap it and not leave any uneccesary wrinkles in the tape, or leaks could occur. Also, when using tape on spots that are sized to fit into their place in the gun, use as little tape as possible.
-If it's the Pressure tank, you will have to open the Pressure thank to investigate.
(In the case of Spheriod CPS tanks, you will have to open the Plastic Ball casing by removing the screws around the edges of the tank. Piston-Cylinder types -I think- will just slide out of their protective plastc guard.) Check the pressure tank, if it's condition is like a shredded water balloon, there is nothing you can do. If there is a pinhole leak, patch it with a Bicycle Innertube patch kit. Use ample amounts of rubber cement. If the problem is still unidentifiable, pump a little bit of water through the system to observe the leakage.

More to Come!