A very familiar situation! If I ever get around to making the videos I have planned I hope that they'll be useful as refreshers.I just played a 'quick' demo game with my gf, but it turns out it wasn't so quick due to extreme rustiness on the rules - lots of flicking through the book looking for answers.
Page 89 of Da Uvver Book1) Where are the rules for Bottle Tests? I know they exist somewhere, but still can't find them even after a post-game look.
By the wording it looks like "without" isn't meant literally. Any kind of effect that renders the driver unable to act as normal is presumably covered under the "or whatever" bit.2) p. 34 has rules for vehicles without drivers. I assume these also apply when the driver is merely down? It does actually refer to being pinned, so I would guess so, but it seems an odd example, because neither pinned nor down amounts to being without a driver.
It does refer to specifically being thrown overboard but by the "or whatever" wording from above it seems reasonable that other incapacitating conditions also apply.3) The aforementioned section also directs you to p. 44 for attempts by other crew to take over the steering wheel. It says that they can do this on a 4+. However, this section only refers to when a driver has been thrown overboard and it seems to be written on the assumption that an enemy boarder is still on board the vehicle.
Again, I would say that the "taking over" rules are probably written to deal with vehicles that are effectively without a driver so yes.3a) Can another model (attempt to) take over driving when the driver is merely pinned/down and not overboard?
Yes. The rules stipulate that drawn combatants can't take over (and those who lose are automatically thrown overboard) so that leaves only crewmen who either didn't fight or who won. Warriors who won their combat will have thrown the losing fighters off. The test represents the warrior trying to get the vehicle under control (further evidenced by the fact that if they fail they get another chance every turn until they succeed).3b) Do you need the 4+ test if there are no boarders present? (It's not clear whether this represents the difficulty of taking control with an enemy on board or simply the difficulty of taking control full stop.)