I was cleaning up some old engine parts today and remembered that it was mentioned drilling out the oil passage plug, cleaning the oil tunnel out and tapping the hole for a threaded plug. I didn't go that far yet, but I sprayed some brake clean several ways through the oil jet holes and was pretty surprised at the amount of crud that washed out.
These parts were from an unusually gnarly engine, but it still surprised me. All that said, the cam bearings look really good and the rest of the towers are cleaning up nicely.
