I noticed a small barely discernible indentation on my polymer guide rod about only 1/32 long kinda like you would take a knife and barely shave the surface. I could hardly feel it when I slid my finger over it so I re-assembled my gun . What would cause this mark and should I sand a certain part to elimimate any friction that might be present? I do have a metal guide rod which I haven't used yet should I install it the next time I breakdown the gun ? Is polymer or steel just a personal choice no advantage to either?