The gears were spare duratrax raze gears I've used about 5 times in there. The case is plastic and when the centrifugal force of the case rotating pushes the small gears to the edge they rubbed, a lot. Without the washer there it created heat and melted the plastic. Like I said before, the other three gears were half way buried in the plastic case as well, it was just a matter of time before they blew out too. I had never seen this before or even heard of it. The diff was filled with 10k silicone and it did not leak, there was no evidence of a leak inside the buggy. It had minimal clay in it from the short run and no oil line inside. When my center diff leaked before it sprayed a straight crud line inside the body and on the brake servo, thats an easy way to tell if they are leaking, where ever the dirt accumulates. I'm not 100% sure how much to fill the diffs, before I used to fill them up all the way to the top then mush it all together, after about 6 rebuilds I found out diffs don't work like shocks, you need some air in there. I have filled them just enough to cover the cross since then and have had no leaks since, they are always full when I change oils. The only explanation can be the four spare washers I had left over last time I redid them.