While at Rausch last weekend, the shift rail cap popped off and drained nearly all of my t-case on Shoot the Moon. I am now hypothesizing that it occurred because of hydraulic pressure. The caps fill with fluid and then when shifting, the fluid cannot exit the cap fast enough and it gets pushed out. While it may not pop off on the first shift, it likely loosened it to the point that another shift or hard bump may eject the cap. This wouldn't occur if the Dana 300 wasn't upside down because no fluid would settle or drain into the caps.
Here is my quick and dirty solution