How fast does your carbon brush wear? What kind of time frame are we talking?
Going through two or three a year is easy to do. Always keep one of your short ones in your car just in case you get forgetful and wind up with one that is worn down to nothing. You will know you are there when the performance of the engine starts to drop off. This is all worth it for the way this timer makes the car run. And while I'm here, Tony Wiltshire if you're reading this, I could use a few more brushes if I can find you at the OCF.