This is my first time changing the oil myself. I have the original owner's manual, but some of the pages which instruct on this are missing. My lower unit has an upper and lower gearcase. Should there be two different fill holes or are both filled from the same fill hole on the side? I understand that I have to use a hand pump, which i have, and that the plug on top of the unit must be removed for proper draining to eliminate the vacuum, and then reinstalled while the pump is still attached to hold oil in place. I'm just not sure if everything is filled from the one hole on the side.