Cleaning out ink from rapidographs

Greetings:

A while back I bought a set of old rapidograph pens on eBay. These are
the kind that look like fountain pens, but have technical pen nibs in
them. They had sat around for some time with ink in them, and now all
of the nibs are clotted solid with ink. I could replace the nibs, But
I would rather not since it is difficult to get the old style nibs
these days.
Anyone got a miracle cure for this problem?