I have some weird "oxidation" on 50% of the underside metal of the playfield (two pics included) whats the best way to handle; do I remove all and tumble? or elbow grease all of them individually? I have ordered a CPR playfield, top side of the playfield is torn down. Everything works, so its certainly not an issue for playing.. but wont leave it looking like that either way just would eat at me after all the work to swap playfields