FX huma regulator install on fx impact

i just want to know if anyone has encountered this problem i tried to install a huma regulator on the 2nd reg position of my FX Impact Mk3 and it leaked out of the trigger guard area when i connected the bottle. i did the following double checked the instructions to make sure that the bevel springs were installed correctly ,made sure that the Derlin washer was installed with the black mark against the regulator adjustment screw plug ,inspected the reinspected the regulator for damage found none and reinstalled per the instructions once the regulator was installed i screwed in the regulator adjustment until it just bottomed out.i pulled and held back the cocking lever screwed in the bottle same issue it leaked . I put back the original regulator it worked just fine am i missing something ?
 
HumaReg.JPG

Did you check the large O-ring on the neck of the Reg body!
Is it damaged?...and/or it there??
Also did you apply thin film of silicone grease on the O-ring too....
Also did you screw in the Reg completely...to seat the above O-ring