[FWB]

some , like yours, 3rd members don't have a fill plug. in your case use the bolt/stud on the drivers side, which is a slight bit lower than the 3 o'clock position as your fill hole, fill the lube up to the bottom of the hole and call it done.
the easiest way is with a suction gun, it will pull fluid out or push fluid in.
they have a little hose end that will fit into the hole when you pull the stud out