your correct that they usually don,t need to be replaced ,
but they are a potential wear item so about every two years I replace them,
just as I disassemble and clean and lubricate all the moving parts
and I darn sure inspect them after and before every hunt or trip to the range.
I also replace springs and small parts at the first sign of wear

https://www.brownells.com/schematics...aspx#r32sid382