The first thing I'd check is for grunge build-up on the stylus. Get yourself an inexpensive jeweler's loupe (magnifier) so you can get really good look at the diamond. Sometimes the build-up can surprise you and it may take a couple of cleaning passes to remove. (Read up first on how to clean a stylus to avoid damaging the cantilever.)
If there is wear to the extent it is causing distortion, you'll probably be able to see it after the stylus is clean.
If there is wear to the extent it is causing distortion, you'll probably be able to see it after the stylus is clean.