I have two pens that I've been working on, and although they exhibit different symptoms, I believe they are both caused by feeds that are too loose. I think both feeds are ebonite from the way they look and feel.
The first pen is a Wahl-Eversharp school pen or Thrift pen, cousin to the Skyline but with a blunt-ended barrel. At first it didn't take up water at all, and I realized it didn't have a breather tube. On installing a breather tube it takes up water, but as soon as I lift the pen out of the water, the water starts dripping out the end of the section almost before I can eject it with the lever. The nib and feed just slide in and the only thing stopping them from going further is some kind of stop inside the feed. The inside of the feed measures 5.33 mm, using my calipers, and the feed measures between 5.02 and 5.13 mm depending on where I measure it and in which direction (it's not perfectly round, apparently). The nib is an Eversharp nib so I assume that both it and the feed are original.
The second pen is a Mercurius, from Italy apparently. In this case the problem is that the outside end of the feed seems to be too small to maintain contact with the nib, and it just doesn't get ink. For this pen the inside of the section measures about 5.09 mm, and the feed measures about 4.91 mm; the feed also has a rather long taper, compared with the Wahl-Eversharp. I tried heat-setting the feed to the nib but it didn't seem to make any difference. The nib is a Warranted 14 Ct. Gold nib, so I don't know if it is original or not, but it does feel a little loose when installed. As with the other pen, nib and feed are easy to pull out and push in.
So that's my story. Can these pens be saved?