I see this topic is nearly 2years old now, however just updating it in case anyone else stumbles across it like I did, ive came across my own thread 2years down the line with another air leak

. my logun solo was leaking air, unfortunately it wasnt from the usual suspect of the filler port valve/ O ring but from the brass valve the other end of the air chamber(I suppose its a fairly crude regulator of sorts) it had air leaking from here caused by hardened o rings and a worn needle valve and valve seat, im from the uk and parts seem regularly avaliable from chambers on the internet, I had difficulty undoing the brass valve from the action bit a bit of rag and a vice it came open fairly easily I also struggled taking the plastic valve retaining cap off, I persevered and undid it/butchered it with a pair of side cutter, all sorted now, glad this rifle is so easy to work on