corrosion below the waterline

My 8”x3” grounding plate doesn’t look right. I know some are porous bronze but this looks like stainless and is non-magnetic. It is only connected to mast and stays not bonded to thru hulls for lightning protection. It looks like severe wormy stray current corrosion even in the machine screw...

Dear Fellow Sailors: I've never had an anode on my 25' sailboat (lead keel). I don't believe I've had any issues with electrolyte corrosion. Any anecdotal or Anodedotal evidence of issues anyone has had are appreciated. Thanks