Has anyone encountered a problem with the "upper" knee joint on Masterpiece Optimus Prime, specif. the 2006 US release with the stand? The left leg has stress marks, the joint frequently pops, and doesn't stay straight if lifted. I disassembled the upper leg, and found that a part of the upper joint had split. I glued that part together (gorrila glue), but it still isn't working right. Any suggestions!?!? Please? I love this guy!