My 250cm tall model of C3PO unfortunately had a bit of a tumble off his shelf the other day. While he initially looked to be intact, only his head had come off but it is only lightly attached anyway, I discovered that one of his thumbs had broken off where it attaches to the hand. Upon closer inspection it appears that the thumb is actually a separate piece that is attached at the manufacturing stage, it was the square plastic pin that it attaches to that has broken off the hand.
The reason why the thumb had broken off was because it is situated very close to the body when the arm is in place, a sudden knock from the right direction would push the thumb against the body, the result would inevitably be a broken thumb.
Rather than simply glue the thumb back on and risk it falling off at the slightest tap, I elected to perform a bit of surgery – I drilled a small hole in the hand and the thumb then inserted a thin brass rod, thus forming a strong link that should prevent any such breakages in future. I hope these pictures will better describe what I did.