Yes, it's not the adapter neither the atty.BUT I know it is not a problem with the GG 510 adapter because the 510 attys from eastmall.net don't leak at all.
So now I only use the 510 attys I bought from eastmall.net - they are only $8.00 and are working AOK with the GG.
I did more tests and screwing to maximum acceptable force with the right tools.
It's the golden cap (ato side) the problem in my humble opinion. It's like the external threading is not good enough for the adapter.
More testing of the 510 before I vote though. Not yet decided. 901 is great too but yes it feels smoother... we'll see. One of the most important thing for me is the taste reproduction.
That's nice to have spare parts ! A small problem but I can still test the 510 with the silver cap