Internal cable routing blocked on '80s steel frame. What are my options? I have a new-to-me ~80's steel frame with a rear derailleur cable that is routed through the chainstay. There's a blockage close to the BB end, and I'm wondering what my options are?

My assumption is that it's mud/dirt/etc. due to where it is, the fact that I cannot blow air through at all, and what it sounds when I jab it with a coat hanger.

This frame means a lot to me, so I'm very keen to get it working if I can.

Edits:


The frame is a (I believe) 1981 Concorde Acquila.
The chainstay holds a bare inner cable.
And pictures added (more for Criggie, rather than solving the
issue, though if click through and zoom in on the second picture you
can see the exit-hole on the chainstay)
I'm sad to say that I solved my issue by adding a clamp-on cable stop much like this one:

.

If going down this route an optional extra is to poke the blockage with such force and frustration that your poking stick (coat hanger) breaks off and is stuck forever inside the chainstay. I elected to go down this route, but my understanding is that it's not compulsory.