We are going to leave the lift again overnight with a load in the car and mark a point on each cylinder stage to identify which one, if any, of the stages are leaking.
We will also disconnect the fittings before the ball valve to see if oil is bypassing and leaking through the seals of the ball valve.
All in all, I doubt the system could hold about 100mm of air in the system, the odd few bubbles that could cause bounce maybe, but not that much of drop overnight would be caused by air in my opinion.
