I am continually amazed at the "Kreosote" (by-product of water vapor & oil vapor) I find on head bolts, and in the head bolt holes within the head when replacing seeping head gaskets.
I always try talking the owners into replacing the piston rings as the same chemical process that fills the head bolt holes also fills the oiling holes within the third ring groove (the oiling ring) on the sides of the pistons.
I always DRILL out the holes and often have to use the drill-press, instead of the hand drill, as the Kreosote plugs are so solid. The purpose of these holes is to supply oil to the oiling rings (the piston bottom acts like a funnel capturing oil sprayed from the sides of the connecting rod bearings at their crank journals). The oiling ring has calibrated openings and two "squeegie" edges. Often these are multiple piece devices which eliminates the large end gap if the segments are mounted properly.
Inadequate oil delivery because of plugged holes leads to rapid cylinder wall deterioration. This is indicated by loss of "honing" marks and the presence of vertical scoring.
Caught early enough, the cylinders can be honed, and the rings, and crank bearings can replaced with hood and block in place. Severe scoring will not hone out, but requires boring for larger pistons. This is very costly and the block must be pulled.

Dan Patzer
the CyberWrench 425-259-3601 72' tii touring K75RT 85' 732i R100RS from BIMMERS ONLY http://www.nwlink.com/~bmrfamly/ O.E.M. parts, Independant service since 1967 12724 Marine Drive, Marysville, Wa. 98271