Perhaps a valve cover removal is in order to verify the sludge hypothesis. I recently did a timing chain on my 2012 and saw a dirty, varnished engine, carbon on sides of oil pump, on the valve cover, on the reluctors of the cams, but no sludge anywhere where it pools though. This was a verified, regularly changed oil every 5k miles or so vehicle. I did not look for return holes. I will have to do this soon before it gets too cold. Yesterday I checked the oil after it was very cool, sitting for hours after shutdown. It was 3/4 full on the first pull of the dipstick. On every other car I have, I don't wipe it if it was sitting for hours. I wiped it on this thing and on the second pull it was just touching the end. I let it sit overnight, and this morning it read 1/4. Something else is happening, I bet it has to do with the filter. I remember the filter not satisfyingly snapping in place on the cap when it was changed a couple of months ago. I don't know, but I will be on this soon as "it is time for a change". (Bill Clinton's line when he was running.)