Oil pressure relief valve

[Saskwatch]

Manual says to “Inspect the relief valve plunger and the spring”  and if going to reuse to “polish” before reassembly. 
   What would I use to polish up the plunger ? I can see where it has been moving back & forth but really no deep scratches can be detected when running your fingernail over them. 
  Thank you in advance,

     ?

[kencombs]

Lots of choices, I usually use 1000 or 1500 grit wet or dry for such things, just because I always have some handy.

[P15-D24]

Crocus cloth

[MarcDeSoto]

Maybe some steel wool?

[Conn47D24]

Soak the crud off, then a fine fine wool