The system should self-bleed, but it may not self-prime. I haven't had much problem with the load leveling systems, but have had the same pump not prime on many full hydraulic cars like the 6.9 and 500SEL.

Fill it up and see if it works. The way to tell qualitatively is to have three people get in the rear then start it up and it shoul lift the car back to where it started.