clogged section on a lovely mabie todd swan (novice repairer)

[profdavid]

Onward to my second repair job, a lovely lever filler Mabie Todd Swan 3150 which I am keen to get back into service.
In my naivety/optimism I anticipated fitting a new ink sac and Bob’s your uncle…
However, the section appears to be complete clogged up (see photo). This is so solid that I guess it must be the remnants of the deteriorated sac rather than just congealed ink. Any suggestions for getting this out, would it be worth soaking overnight? I have tried gently to pull the nib/feed out but they are stuck fast.
Thanks very much for any advice.
Attachment 54123