It's interesting that the OP did mention Campagnolo cranks for possible buffing out, as Super Record cranks are notorious for cracking at the spider and arm junctures. Some early Mavic cranksets (the fluted non-starfish ones) supposedly had similar problems. Most attribute it to sharp corners at the crank and spider arms juncture that could have been rounded or "eased out" during manufacturing to avoid any stress riser situations.
Other than that, the only areas I've heard of cracking on some cranks is right at the middle of the main arms when a nick or gouge on the surface supposedly propagated right through and across the arm, causing them to break suddenly as most owners never see the crack or most of it was developing under the surface of the crank arm. Some also suspect that these mgiht have been also caused by bad casting/forging at the factory but both theories have not been disproven so far.

Chombi