i had the same problem with one of mine, and it went to the garbage pile. don't want to waste CO2.............
my HBC makes pre-chillers for their immersion chillers out of "junk" corny kegs. the club blacksmith welds on hose fittings where the posts are. then, they dump a 7# bag of ice in it, fill with water, and wha-la! big ol' pre-chiller to hook up the immersion chiller to. works great too!