Heh. I was dealing with allens that had already been stripped out by whoever was there before.
One, though, I doubt I could have gotten it anyhow. It's the one that holds the suction/discharge hose assembly to the compressor manifold. I got it (finally) with one of those Sears rounded-bolt sockets. Both hands on the foot-long ratchet handle and it was all I could do to break it loose. A hex-headed bolt went in that spot with room to spare.
It's not so much a space-saving measure. Allens, Torx, Robinsons, and such are easier for automated assembly-line machines to deal with.