Buffing is the last thing you want to do. If you want a mirror finish use 1000grit or 2000grit sandpaper. Have to be careful if the metal is already thin or not. After you sand it it should be automaticly a semi mriior finish then you wax and buff.

Take it from me I have done this countless times with automotive parts. Come to think of it heres a guide a friend of mine did with a heatsink for his gaming PC a few years back.
http://www.overclockersclub.com/guides/heatsinklappingguide.php
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