Although I have the tools and I can use a friend's machine, I elected to superglue a 500 grit wet-dry sand paper, cut it close around the outside and patiently went back and forth for an hour with it, until it was even and there was not sign of any scratch even looking it with a magnifying glass.  
Then I used the Permatex "Copper Spray-a-Gasket" to install the compression gasket.  
This way, I sleep well.
Zoltan