Since we obviously have members who know their oil bottles looking at this thread, perhaps somebody can identify the lower of the two oilers which I recently found at a flea market.
It is here compared with a standard Mk.IV and is too long to be a modified Mk.I. Its lid and dipper are identical to those of the Mk.IV and apart from a B.S.A. logo stamped on the bottom with a "40" on the side is unmarked.
It fits nicely into the butt-trap of a military No.1 or No.4, but once inserted there is insufficient space for a pull-through.