Morning Julian looks we can restore that ok, if you say the knot comes out quite easy then this is the major part out of the way, sometimes they are a pig to get out, I don't restore a lot of brushes but always give a look first Julian and in this case looks like I might be able to help. Let me know what your options are in regards to knots, if you can remove the knot that would be great I will do the clean-up and re-knotting, if it is a stubborn knot steam will help a great deal. see how you get on. Let me know.
Mervyn