Its fiddly but you can change the actual brushes in the end bell kits. Been doing it for years. Just snip the wires and remove. The brushes I get from my local vacuum cleaner/washing machine spares shop. If you cant get the exact size brush a bigger one can be easily filed down to correct size. Then new brushes can be soldered to old wires. Believe me it sounds like a botch but it really does work and has saved me 100's of pounds over the years.
Chtis