I recently bought a pair off E-bay which did not function properly. When I disassembled them I was quite surprised at how complicated the insides were. It was like a three ring circus in there. However, I cleaned every little thing, no matter how bizzare it looked, and put it back together.

The cleaning made the functionality about 90% better, but I still have some problems, so I'll have to go back in sometime. One day I hope to play a 5200 without any controller issues.