The older dice are normally the ones with the condition problems. Dice used to be made with cellulose nitrate...material similar to what old film was made with. Unfortunately, the material isn't stable, and it's flammable. Dice that appear to crystallize (cracks all through the dice) are cellulose nitrate. The crystallizing dice can be coated with clear nail lacquer, which will slow the deterioration.
Vinegar syndrome (dice with a strong vinegar smell), and "imploding" dice...which look like they're caving in, can't be preserved as far as I know. I tried coating a pair with nail lacquer, just to see what would happen, and I was left with a sticky pair of imploding dice.
Segregating your deteriorating dice is the right way to handle them.
I found this article online, which explains it better...
here's some of our damaged dice...