Do trackball balls need cleaning, and can they be replaced?

Yes. Trackball owners across specialist communities note that the ball and its support bearings collect skin oils and dust, causing 'stiction' or grippy movement, and recommend periodic cleaning. Replacement balls (such as 34mm aftermarket balls) are widely available and fit many popular Logitech, Kensington, Elecom and Perixx models, letting owners swap in smoother or differently colored balls.