I'm sorry I don't know the bleed and refill procedure, but I have experienced similar problems with the leveling system on a couple of 300DT's. I fixed it perfectly by adjusting the actuator lever attached to the control valve and linked to the rear suspension. Just loosen the lock and move the lever until it's at the height you wish.

I would expect that if you filled the reservoir, and kept it full, normal driving would eventually bleed it.

Good Luck