K now there are 2 things that can be alloy. i have the HPI alloy diff cases that hold the spider gears and i have the FLM bulks. Between them and properly shimming i have yet to replace diff gears years i have had the truck. Ans the flm bulks have only been on for about 6 months.
The hpi alloy diff cups (hold the spider gears) are a must. I also plan to buy the flm combo case/bulks for my flm chassis. Shimming the ring and pinion properly is a must for any vehicle, especially a heavy monster truck.