If the scratch can get in the lid then sanitizer can too. A scratch means nothing.
Your talking to someone that is scared to death of germs! I wouldnt make a habbit of testing scrathes on plastic but..... Just do what i do fill the bucket up with sanitizer and cram lid in there and soak for 30 minutes. Im not dead yet and beer is fine. Its kinda like saying soap cant get in creases in fingers. Your good