Most likely you are over oiling your mags. That oil gets blown out the mag into the blowback chamber every time you fire, which isn't bad for the gun, but does tend to coat your hopup bucking with oil, making it far less effective than it should be. And it leaks out everywhere. You only need to add oil to the mags once every 8-10 fills, at most. I actually don't add oil to fills, I oil the mags while they are empty and then fill them and hit the valve to blow out any excess. The seals only need a very small amount of oil to stay properly lubricated.
Another possibility is that it could also be oil that was intentionally put into the hammer and trigger mech to lube it, that just hasn't finished working its way out yet.
When I work on a GBB pistol I always shoot a little spray (low viscosity) silicone lube into the hammer and trigger mech and then cycle/work them repeatedly, feeling for grit or dirt in the mech, until the lube doesn't come out any more. But I only spray a very small amount in there and I clean it up after, someone at the factory may have sprayed a lot of higher viscosity oil in there and it's just taking a long time to come out.
But most likely it's you overlubing your mags.