In the small block tech archive the is a post about changing oil pumps. About halfway down it talks about how to check to see if the plug is in there through the oil sending port using a small rod. It has the dimensions for how far the in the rod should slide in. The plug diverts oil to the filter. That plug is the DEVIL! Can you image pulling it apart and never finding any reason why it ate itself, because there would have been nothing wrong in the bearing assembly, it would show pressure, you would finally chalk it up to that mystery "issue" putting it back in and if does it AGAIN!!!