Third hole in 1st gen diff cover

I just recently pulled the rear end from a 2002 Tundra Limited TRD parts truck. I see that there's a third hole in the differential, it's not the fill or drain plug, it has a sort of rubber thread on it. Any ideas what this is?

 

I just flipped thru the 00-03 FSM and I'm not seeing that in the suspension/axle section. The way the paint is flaking off around the grommet and how it's dented-looking makes me think it's not OEM, but I don't claim to know everything about every make/model/year/provision.

 

Maybe the drain is stripped?

 

Almost looks like it's welded shut (edit: the fill plug). You'd think the seller woulda mentioned that though, no? If not, what an AH.

 

It’s too big and in the wrong spot for any add on air or electric actuation plumbing for a locker. I’m going with the above theory that the drain is stripped or otherwise fuckered and this is an auxiliary drain hole made by a PO. Or a POS depending on your assessment of this “mod”.

 

some junk yard employees (such as some pick-n-pulls) will use a air chisel to quickly punch a hole in a fuel tank, transmission pan, engine oil pan, axle diff, ect (in order to drain the fluids). Some times a rubber brake bleed cap then gets pushed back in to seal it back up. I get SUPER pissed when i go to junk and see that sort of laziness!