No, this is not normal consumption. When you say valve seals, I'm assuming that you mean the valve stem seals. On a car of that age and mileage, I would consider the valve stem seals the primary culprit. Since you've had your's replaced, I would then check the rear main seal, head gaskets, and valve cover seals.

I don't know what type of oil is "best" to use. I use Pennzoil 5W30.

__________________
Mike Heath
1988 560SL Black/Palomino
1988 300SEL Black Pearl/Burgandy
1984 500SEC Anthracite Grey/Palomino