Have someone with an experienced eye look at the stylus under a low-power microscope. Signs of wear will be easily apparent.
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Take a post it piece of paper. Place the stylus on the paper (lay the paper on the table mat, but do not turn anything on). Genltly turn the platter so that the stylus passes over the paper. If the stylus catches, or scrathes the paper, it probably needs replacing. It should go over the paper smoothly and not snag along.
Otherwise, take it to a dealer who can look at it under a scope.