plastic diffs but I have never done this. I have run the diffs in stock and mod. In fact, I'm running a brushless in mod mode with no problems. Are you sure your not running them too loose with not enough grease? If they are loose it causes them to spin too much and heat up. I compress the spring all the way and back it off a 1/4 to a 1/2 turn. I would just use the steel ones if your running mod. More and more I'm thinking the lightened parts are not worth it. Other than maybe some good bearings, graphite kit, lightened screws and plastic cvds. Other than that the rest is for the birds.
I would rather not have to worry about breakage.