I changed the fluid in my lower unit and I lost a little more than what I would like before I could get the screw back in, so after letting the fluid settle awhile, I topped it off with a touch more at the top vent hole and let it settle out to where it seemed level with the vent hole. I assume you fill from the bottom to prevent having any pockets that might be missed by filling from the top, but does it hurt anything to top off at the top vent hole, just to be sure you have it full? I am very particular about things and I just want to be sure I get the right amount back in. How particular in the amount do you have to be or is it really just an approximate amount? I appreciate the help.