So that's what it's called? So yeah, I just applied silicone grease to the gasket and the surrounding areas like you said but it's still leaking. Could it be possible that the output valve for my gun is broken?
Anything is possible, but anything can also be fixed
. Make sure that you put the mag back together correctly and tight, because the silicon grease can cause problems like o rings / gaskets slipping out of place during reassembly. They can also swell up when they absorb the grease, causing slight fitting issues.
This is normal (the swelling plugs leaks), but it just means that you have to take extra consideration when reassembling (read: just because you put it back together the same way you took it apart doesn't mean everything inside is correctly aligned).
If that doesn't work, then I'd say the next step is to either replace the o rings / gaskets, / flow valve, depending on where you hear the leak. If you don't know where the leak is coming from, you can always fill your mag with gas, then place it under water and watch where the bubbles come from. Sometimes the sound comes from a different area than the actual leak because it may be flowing through / around silicon and gaps and whatnot.