I have a method for cleaning brushes used for 7008 (and other things).
1. Paint the varnish out onto scrap material as far as possible.
2. Rinse the brush quite a few times in as small amount of reducer or thinner as possible. Each time use just enough to wet the brush well. The brush should appear clean after this stage.
3. Wet the brush again with reducer. Wrap the wet brush in a couple of layers of old cotton sheet, in such a way that the layers of sheet are in close contact with the brush.
4. Leave to dry 24 hours. The brush may be slightly stiff, but softens with flexing it a few times before use. It is then good enough to use for further coats, though repeated coats will eventually stiffen it too much.