Dave,
Our engine has oil cups and inside there is a wire handle with fiber wrapped around it in each one, which sticks though a hole to bleed out the oil. This is what makes the "calibrated" oil leak. As time goes by you will notice while servicing the locomotive, that some cups run out faster then others or the other way around. Then you replace the fiber with new so it "leaks" correctly.
You can make it leak more or less by how course of fiber you have on the wire.
I really like hearing all your tales along the ROW. I have done some exploring as well and have found many artifacts. It is neat to look at the parts of rusted metal and wonder how old it is, who all has touched it , when did it fall off or get "lost" etc.
Dan