threaded opening between Cummins and Allyson Transmission

This is awesome getting so much help so fast! It still strikes me odd that it would be threaded but nothing screwed into it. I will leave that for now and focus on the leak first. A thought just came to me... When you are working on these monster rigs, should I completely air it up, as it currently has the air let out of the bags? Jacks down? Advice continued to be appreciated!