I actually solved the problem I think. No, I didn't have any change in performance I could tell, just the codes.

When I cleaned the EGR valve, I noticed that the bolt further in towards the engine centerline was barely hand tight, and the gasket was a bit ragged and had some carbon right at the edge near the loose bolt. With the new gasket and properly tightening down both bolts, I think I sealed my leak path.

It's been running great with no CEL since

However...that tool really is too cheap not to have...