SailingVehicle,
I grabbed a quick photo of the vacuum accumulator when I put the Axis in storage earlier today. It's located a bit left of center and toward the back of the compartment when looking into the engine compartment from the front. It's very easy to see/reach.
Here's the pic:
The accumulator is the round ball with a black and red vacuum hose attached. The black is what became disconnected in our coach. I didn't trace it, but the red should go to a vacuum port on the carb. The bulge where the red hose connects should be a check-valve that prevents vacuum from "leaking" when the engine isn't running.
If your selector doesn't work at all then one (or both) of these lines has probably become disconnected (could be at either end) or is damaged. If the selector works in some positions but not in others then one or more of the actuator lines is more likely the problem.
Regards,
Randy