I’ve had a DC25 for many years. The brush rotor has recently been stopping after a few seconds; this happens on carpets and on hard floors. If you press the brushes button (the one next to the on / off switch), the brushes turn again for another few seconds. If you keep holding down the “brushes” button, the brushes will operate continuously, until you let go of the button. I’ve cleaned the brushes roller, taken it out & cleared any possible dust, put a small amount of silicon spray lubricant on each end - it’s made no difference. Any thoughts on what the problem might be?