Not necessarily. You don't actually need the fluid to be perfectly sealed out, just slowed down a lot. This means that you could run it open but with very close tolerances and there would be almost no leakage. You just need to make the gap small enough for the leakage to be trivial.

As for magnetic alignment, that is all about maintaining smooth operation without losing efficiency to friction. Instead of a guide with friction you could use magnetic attraction to keep things aligned.