I was in the same boat as you. I ended up buying a used soda keg from the homebrew shop. I just could not get my old 1/4 clean enough. The hole in the top is pretty small and it's tough to get a cleaning brush in there and then all around inside. I've washed mine 3 times and it still smells like Miller a little bit. For $35 for a Corny, I didn't feel it was worth risking a batch of homebrew that cost me $35 and 2 weeks to make.
But, to answer your question,
check this out. You'll want this kit for the snap ring. The retaining ring that's on your keg now will be a b!tch to put back on, trust me.