Recently purchased a Pilot Super80 on Ebay but it arrived with absolutely no instructions on how to fill. If I unscrew the body it has a metal core and some type of lever on the end. Does anyone know the proper way to fill a Super 80

It's pretty simple.

Dip the pen into an ink bottle and move the lever horizontal, then vertical, a few times. It should spring vertical as there is a small spring inside. It is refuses to move or needs coaxing, you probably need to replace the sac.

It is usually fairly simple to replace. The chrome sleeve comes off and the bottom of the sac on the nipple is exposed. You will need to clean out the inside of the sleeve as there might be parts of the old sac inside. Even if the spring is broken, the pen can still be used by moving the lever aside and up a few times.

On some of these models the sac is fitted inside of the section and difficult to replace. You will need to have it done by someone with repair experience.

Good luck.