When to replace knock sensor?

[Mist3r Spool]

Is there a time/mile interval for swapping out the knock sensor? I have 164K and am thinking the missing link to better performance is a worn out/old knock sensor (which is possibly retarding my timing). Any takes? I've searched and just found replacements and how-2s.

 

[DevilSperm]

I dont know about a time interval, but if the black shit on the back of it is gone or rotting away then thats a good sign to change it