It would be good to know the date-code on the back of this crank, can you please post it, Rob? <x> is a 1970's year, (y) is an early 1980's year, [11], [22], [33] are 1985,6,7. There are some other codes but not for this crank, I believe. If it's a very early crank (pre-BMX) we can probably guess that it was anodized in the after-market.
1970's campy cranks had the flutes milled into the crank arms. I have seen some later cranks that had the flutes forged into the crank arms.
It seems possible that the crack originated from the very tip of the milled flutes of the crank. This was either the starting or the ending point of the milling drill. If this area was not carefully polished at the factory, before anodizing, it could have left a scratch or a crack that could possibly grow later in the life of the crank.
Personally, I think the actual cause was the crankset reacting in revulsion to the clipless pedals, but that's just the retro-grouch in me ... :-) :-)
- Don Gillies
San Diego, CA, USA