I wouldn't count too much on metal to deal with the brittle plastic problem Richard. Several years ago I was acquired some figures painted by someone who did work for a museum. Over the last couple of years we've noticed problems with some where the metal is starting to deteriorate. Friends into model RRs have told me similar stories.
Figures shouldn't go bad in 5 to 10 years. If it was a serious problem though I think we would have heard much more about it by now. The most likely explanation is that there was a bad batch of plastic possibly exposed to adverse environmental conditions.