[the bradster]

Hi experts I'm new to this, i usually consider myself pretty handy but i'm stumped, all of my connections are tight and sealed shut, the source of my leak is actually around the post of the plunger, upon turning on the CO2, which is set correctly, gas streams out around the entire base of the shaft that's pushed down when you tap the keg, it's a usedkegerator, i just want to know is is somehting i'm doing or do my roomates and i need to buy a new tap, thanks!