If your cylinder needles aren't broken, but the latch simply sticks every once in a while, then you can repurpose the needles into pick-up tools for knitters (hand-knitters as much as sock machine folks). Get some of that bake-to-set sculpey or fimo clay, and fashion handles around the bent lower part of the hook.
I turned a bunch of slightly-less-than-perfect ones into pick-up tools for knitters -- made great gifts for my knitting friends, and had the rest in my booth at shows so I probably re-couped my expenses :-)
I've also seen "stitch picker-uppers" for sale that are either these or knitting machine flatbed needles with handles on them -- wood handles, clay handles, or soldered onto a longer piece of metal (now, those are very handy with sock machines!). So if the idea intrigues you and you don't have imperfect sock machine cylinder needles to play with, look for these at your LYS.
If you really want to try to re-use the needles -- I admit I never do -- try a magnifying glass and some of those needle-nose tweezers -- there could be some miniscule hairs trapped under the latch. Or a short bath in solvent to route out the same, followed by an oil bath to re-lubricate it. I'd mark it with a permanent marker, though, and put it on "trial" in the sock machine so you can easily remove the needle if you find the machine still spitting stitches or catching yarn in a funny way.
(based on a post by me on sockknittingmachinefriends, 21April2007)