Yah, you can usually spot leaks ... but not always. If the leak is out by the wheel, the oil may get blown away before you'd notice. Murphy's law does apply to the VX.
Remember a sage piece of advice though: ALWAYS remove the fill plug first, NEVER the drain plug first - just in case you can't get the fill plug out. Ya can't drive with an empty differential. IIRC, credit goes to etlsport for that one.