[Yukon Jack]

"For all I know, someone may have intensionally broke the case there to let gear oil run back to keep the coupler from drying out like others have said tend to happen."

Haven't heard of that issue, on my adapter, there is a hole in the bottom of the adapter between the holes that the crossmember bolts to that would let any oil that got into the adapter flow right out - so at least for my adapter (for a Rockwell and CH465) that wouldn't do much good.