[SilentScope]

There are two pins on the side of the magazine that you will need to pop out. Once they are both out, lift the upper plastic portion from the back end and allow it to swivel upward. You should see a large spring in the middle of the magazine housing right below the portion you just lifted up.

The spring is either out of place (I'm sure you can fix this if this is the case) or the spring is broken/missing. Let me know what you see as soon as you lift the upper plastic portion.

 

[SilentScope]

Ah, well if the seam has split there's no other option than making it stick back together with tape or glue as you stated. If I were in your shoes I would try tape first and if that doesn't work too well, super glue as a last resort. Or super glue + tape >.

If you plan on super gluing, try cleaning whatever you're about to glue with rubbing alcohol. This should allow maximum adhesion.

 

[SilentScope]

Grease really shouldn't do much for the magazine in theory, and
I've avoided greasing the magazine because grease in the magazine would lead to...

grease in the mag well, BBs, hop up, bucking, inner barrel, and finally this all leads to bad accuracy and FPS consistency. All in that order >