[pushkins]

The secret with what your doing is to power wash the deck with a good cleaner then wait until it is completely dry, this may mean anything from a couple of days to a week. When any part of the wood remains damp/wet the stains/ sealers penetrate at different levels and hold the wood fibers differently. So make sure the deck is dry before applying sealers/stains.

Yes if you use a solid stain it should cover problem areas, always remeber though a stain is just that, it stains and to do that it is absorbed by the wood, different woods will absorb differently just like knots won't absorb as well as other places on a plank.
Priming and painting will most definitley cover the problems, but my advise is to try stain first.