ill post out the mod around monday.
im not home and cant upload pictures.
ill try my best to use words to describe it...
shave the O-ring really thin... almost 1mm thin.
take your hop up unit and disassemble only the bottom and centre gear.
now put back your centre gear first, but between the centre gear and the hop up unit, put in the O-ring you just shaved.
now screw back the bottom gear. try to make it screw on somewhat tight, too tight will make it impossible to adjust the hop up.
what this mod does is, it creates friction between the hop up unit and centre gear so that it won't back down.