The SME series III is a good tonearm, circa early 1980's. It is still a good tonearm! The fact that it is mounted on a Rega P3 (circa late 1990's) lends me to believe that the cartridge is probably good, and so should be the stylus. You could examine the stylus for wear under a stereoscopic microscope if you have one available. One might be available at a local high school science class or college science department. If I were you, I would clean it carefully first, make all the fine adjustments as needed, and then assess needs. It sound like you got a steal. Happy Listening.