I thought I share what I did today.. Have you noticed the o-rings shredding or breaking underneath the screws for the magazine? The o-rings are very hard to find, since they are small. I checked Crappy Tire, Home Depot and Home Hardware and no one has the exact o-ring size.. I went to the dollar store, and I found these donut shaped nubs as part of an eyewear set... Here is a picture of the nubs on the right:
Notice how the original o-rings (left) shred and tear easily, esp when compressed by the screws.. the nubs (right) are MUCH better, more sturdy.
I slightly sanded the outer diameter of the nubs with a dremel so that each nub is exactly has the same dimensions and fits perfectly into the holes on the backplate. Notice how the nubs are cylindrical and form a better seal as opposed to the o-rings which are shaped like a donut. Also, the nubs are firmer so it doesnt deform easily under pressure for the screws. The nubs are snug in the slots of the backplate, and can be compressed by the screw to form an airtight seal.
I think this is a better alternative then buying them from airsoftbuddy which the shipping will kill u. I paid $1.50 for 4 of these nubs which were part of an eyewear set.