Like most have said already, the tranny is lubed primarily by sump oil "splashed" up from the gears up into the interior, and being "heavier gear oil" it coats the parts and drips back down to the sump. A lot of the oil is left coating the parts when you drained it. Running it probably did not harm things if the overall heat was not too bad, and your putting in the oil quieting the whine immediately is actually a good sign. Long term effect maybe reduced life...but that would depend on when you do the next drain how much metal is captured by the magnet and time. :s