I had a Schwinn Paramount that had grease soaked rags in the tubes - seat - down - chain stays. The way I found this was when I put it in the parts washer , the solvent would not flow through the tubes, I used a "screw type valve packing remover" to remove the rag packing. I have NO idea why it was there. Dampining any vibrations? O yes NO RUST inside any tubes.
Still Puzzled.
Charlie Petry near Daleville PA USofA