Ben Franklin forgot about leaky gas airsoft magazines when he said "nothing can be said to be certain, except death and taxes." Leaky gas airsoft magazines are a sure thing. At some point, it will happen, even if you own our exhilarating HK UMP GBB submachine gun. What happens when the inevitable occurs is entirely up to you. You can either toss that salvageable magazine in the trash (don't you dare!) or go pick up one of our HK UMP GBB Mag Rebuild Kits. Fix your busted UMP magazine at a fraction of the cost to replace it with a brand new one. Adding an HK UMP GBB Mag Rebuild Kit to your toolbox is most certainly a good idea.