I don't think that it does dry out. New cpus come with a 'sticker' of conductive goop - a very thin film. When we take the cpu off the heat sink we muck it up and it does look very dry, but if you push it around with a warm finger it becomes much softer, and I think that's how it works - heat softens it.
Anyway, if you've wiped it off and have to put new on, the pea is the size of a petits pois, not a garden one.