i just took apart my wg

the piston is threaded at the top and held on by a "shim" and then a bolt. It looked like the bolt was screwed on too tight. i took off the bolt and noticed that if i dont srcew it on all the way then the piston/valve goes down all the way. id it safe to use a washer or two so that the bolt wont screw on anymore .

i just noticed that no matter how far i push the valve down (even past the flang) the is still VERY VERY VERY small amount of light. Ok well it def needs some type of o-ring i can see the space> Is it something i have to get from turbonetics or can i pick it up at lows?
Thank you