The general consensus is that the passages were too small/ too close/ to little flow near the high heat parts of the block. That would cause conventional motor oil to bake, or "coke", further reducing the available flow through these hot areas. A process that will feed on itself till oil starvation causes failure. The timing chain tensioner also relies on oil pressure for its operation [another common failure on these motors]. Reduced oil pressure to it causes the chain to slacken, and then catastrophic failure. I dont see that rodding the passages is possible with the crank in the car, but if the issue is near the oil feed holes in the crank, then some poking around with copper wire shouldn't hurt it. In some of the forums discussing the fixes for this motor, flushing was discussed as a double-edged sword. It may remove crap, but that means that the crap is now mobile, and may end up in a smaller, or worse spot! The one thing that was agreed upon, was the use of synthetic oils due to their great resistance to thermal breakdown. If anyone reading this has more advice, I'd like to hear it also. Sorry to bring you down with the info about this motor. You started out with a simple repair, but now you may feel like you have a time bomb there.
