P0401 is not the worst code you could get. The low flow could be caused by the valve being blocked or the small tube going from the valve into the intake being blocked. You can easily clean the EGR valve and the small tube yourself. Do a search here for EGR cleaning. It's quick and easy.
Check out this thread- http://www.vehicross.info/forums/showthread.php?t=19092
If you put a quart of oil in with it only being down slightly on the stick, you may be overfilled. A little overfill is okay, but you don't wanna be way overfilled. Then the crank will be hitting the pool of oil constantly causing it to foam. Then you'll get air in the passages with the oil, meaning there is less oil circulating, not good. Just check to make sure you're not too much over the full mark. Checking cold or warm does not make a huge difference, as long as you're on a level surface and you wait 5-10 minutes. You could easily pull the plug yourself to drain a small amount if needed or just get a full oil change if you doubt the dealer did it.
Mark
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