The manual spec for flatness of the gasket surface of the head is such that you should not be able to put a 0.003" feeler gauge anywhere under the head when it is placed on a flat sheet of glass. All of the ones I have checked after using the sandpaper 'n' glass method have been less than is measurable with a 0.001" feeler gauge. I'm not sure how you'd see 0.001" with a laser line...
I have also had to fix a couple of heads that had the gasket surface milled yet was somehow not flat. In order to mill the surface flat on a head, the head must be clamped to the table so that the end mill is normal to the surface of the head, which is easier said than done. Not everyone has access to a milling machine, either, and the surface finish is much better with the sandpaper anyway.
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