In almost any head, the oil drain holes will be in a low spot. On V-8 engines, where the heads are mounted at an angle--they are on the lower side of the head. As you're looking at the head (with the valve covers off) just keep in mind that the oil should settle at a low point before draining. If it's that sludged up, the actual holes might blend in with the bottom of the head until you get it cleaned up some.

Hope this helps.

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Earl McLain
'02 C230 Kompressor
'89 560 SEL "Frau BlueCar" (retired April 2004)