The first vintage pen I bought (about a month ago) was going to be a simple restoration project but has become more difficult than anticipated.
When I got my Conway Stewart 475 it had no sac and the nib was bent, these two problems were fairly easily corrected in a short space of time. Upon eagerly filling the pen I suddenly came upon one very annoying problem, when held vertically the ink builds up either side of the nib/feed and drops out of the pen... My first reaction is to check for sac leaks, secondly I look at the feed and nib to make sure it looks OK, thirdly I try manipulating the nib and refilling but none of these offer any solutions... lastly I decide to knock the feed out of the pen. With the feed out all looks OK, the nib seems an OK shape and everything is clean so I reassemble and try again, but it still leaks. After this I knocked it out again and checked the feed and nib in more detail making sure they contacted each other properly, it does seem there may be a gap but I don't know if this is the problem so I take a bit if a risk and carefully put shellac on the areas where I feel gaps may be present, then I reassemble and try again...
It still drops ink so I have taken it all apart again cleaned off the shellac and am left with a pen that would appear fine but as soon as you try to use it it does not hold ink.
Has anyone else experienced this? What may be the problem and how can it be repaired?

Thanks in advance