I've only seen a few of these. This is the first type US Army TSMG three cell mag pouch for XXX magazines, loosely patterned after German MP40 pouches. XXX mags are a tight fit! Both types of oiler fit fine in the space provided. See page 353 of Tracie Hill's book for a photo. The one in my collection is in new condition and is of a medium green different from the more typical OD shade #3 or #7 period canvas. The black leather is correct as well.
Someone just might get a bargain. Either that, or the snipers will be out in force as the auction ends!