Faulty gaskets
After 1 game and a month in storage under pressure, silicone oil leaked from both gaskets, I had to disassemble 2 magazines, 1 got fixed with some silicone oil replacement and tightening all the screws, and the other still is leaking from the top gasket. I am not sure if it's just a lemon or if those BCM mags have poor QC but be aware when buying - there could be an issue with sealing.