Codes P3190, P3191 after replacing EGR cooler, egr switch, intake manifold

A few months of driving it with the shaking, I finally had some time try to figure out the shaking and exhaust fumes in the cabin problem. I took a good look at the old intake manifold, and noticed an intricate red rubber gasket. I didn't remember installing that when I did the work. I looked back at the pictures I took along the way, and sure enough, the new manifold didn't have a gasket. I purchased one, tore it down, installed it, and the shaking / exhaust in the cabin problem is gone. It has been about 2 months now, and the car is back to running flawlessly.

There is one odd thing. It seems to be using coolant. It's very slow, but I have noticed the "cold" level drops a little every month or two. I've checked the oil, and it is normal, not cloudy or milky at all. Is this normal for a car at 220k miles? Is this something that portends trouble, or just an old car thing?

On a side note: I recently had the check engine light come on immediately after filling up the gas at one particular station. The station's pumps constantly trip the fuel stop function, even when it isn't full. This happens no matter how slowly I pump. I end up having to coax it to full. Apparently, I filled it too much, and it caused gasoline into some system that should only circulate fumes, and it caused a P0420 code. I cleared the code, and I won't be going back to that station. It is a bit ironic and hilarious that the fume circulation system would throw a 420 code.