If so, almost all versions have suffered from the dreaded knee/hip click, some people have reported relief (if only temporary) by “manual repositioning” of the leg/knee in question. If you have it deskinned, did you notice any foul play around the wires going to the position feedback pot for the knee at the bottom of the leg. If you raise slightly the “wire clamp” over the top of the pot in question, you can see a tiny white flat shaft that should rotate as you “reposition” the knee. The wiring going to the pot has a great glob of hot glue (usually) which can sometimes conceal a broken or partially failed connection.
If is the whole leg that is not moving, then the pots are on the servos on the leg motors (more disassembly required). The clutches are dead simple (a spring holding two gears flush together until the torque overcomes the spring force). They don’t fail as far as I have ever seen. I did take one apart, putting back together was another story. It has a tiny circlip that holds the spring and I only have two hands! >:(