Should this "drain-like" opening in my Allison tranny have a plug in it? Looks like it's in the bottom of the torque converter area. Bought MH used. Any thoughts? Thanks all.

No, this would drain any oil from a leaky rear main seal or trans torque converter seal. When my rear main seal went south, I put a small pipe to the rear so I could collect the oil, but it is normally open with no plug.

Great news. And no drainage apparently. Thanks for your help. I don't know what I would do without this forum.

You'd be paying someone big bucks...