I can't speak for Rod, but everyone back home has had diff issues, and we're talking about Tamiya enthusiasts with years of kit building experience. Likewise, Gary and Jeff were both telling me about all of the stories they had heard from customers that also had problems with nuts backing out or thrust bearing failures. So much so that Speedtech was well stocked with diff screws and thrust bearings, because when you melt the plastic halves you don't get the hardware back easily.
It may help that Rod (1) is a very clean driver, and (2) rebuilds his car after every run (or so it appeared). I believe he even had a spare diff or two laying around this weekend.
There are a few tricky assembly instructions where you flip the diff around, but even following those instructions perfectly the diff may still fail. It may be a problem where we have over tightened the diffs, but I don't really know for sure. I didn't think I had cranked it down.
Hey, it's just my 0.02. Take it for what it's worth.