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OK, that I would believe. Unburnt fuel, blowby, etc. probably recondenses into stuff that looks like oil. The piston to head clearance is fairly critical in the high compression flatheads, and won't tolerate much milling, as a whole day spent with a die grinder to restore the clearance will attest. I agree with Zane that milling the head isn't necessary in most circumstances. Use a good gasket, the proper fasteners, torque them properly in the correct sequence (50 lb-feet with grade 8 bolts and teflon thread sealant is my personal recommendation). If you find the head warped, and feel like you must shave it, check the block as well. If the block is .005 out of flat end-to-end, do you propose to shave it as well? If not, does one flat sealing surface really help? If the head or block is really badly warped (say .020), or there is localized damage (scratches, erosion due to blowby into water jacket), then shaving may be necessary. But take off the minimum amount, and check your piston to head clearance before assembling. New cylinder heads are not that expensive. Overhead valve heads are much thicker and less flexible than the flathead. It is more necessary to shave OHV heads when they are not flat. Generally, the piston to head and piston to valve clearances are not as critical as in the 8N engine, so it is also more feasible to shave them.
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