I currently have a Shelter 501 cartridge with approx. 1500 hours. It still sounds great but when is a good time to change or re-tip? A very reputable cartridge maker mentioned that 2500 to 3500 hours is common when the unit has a real diamond tip. They mentioned a sure way to tell the cartridge has given up the ghost is when extra dust becomes apparent on the record and on the cartridge. This is not from the normal dust build-up. I would rather not spend the $$$ on another cartridge or retip unless needed.