Is it fairly easy to inspect a plug and know if it needs to be replaced? They'd be covered in oily gunk, right? Or might they not be and still need to be replaced?

 

I know what the book says, but I have owned many rotarys and never gone over 20k without adj or changing them. I have over 16k now and would love to pull them and inspect. Has any one done this and what did they look like and how hard did they drive them?