Based on some of the comments, I took a closer look at the tapered inlet/outlet end of what we now think is a hand pump. As can be seen in these new photos, there are a lot of thin, circumferential scratches or indentations in the top and bottom surfaces of the curved nozzle. looks like this may be evidence of the nozzle repeatedly coming into contact with the sharp edges of a threaded hole. I could easily see this happening when pumping fluid into or out of a gearbox or differential.
Thanks very much for the great replies. Please keep them coming, if there are any more thoughts. This forum is really amazing and I appreciate the help being provided.