Rockola Needle Question

I have a Rockola 448 that I put a new needle in back in 1983. It has played 16,000 songs since then. Still sounds good. Is there a "rule of thumb" as to how often to replace that needle? Thanks

Johnny,
My "rule of thumb" --if needle pressure is correct, 45 rpm phono's-- 20k is about the limit for sapphire, and 100k for diamonds. Ron Rich

Thanks Ron...