e34 self-levelling suspension - how fast does it react?

[sideways500]

I've just bought a 525 iX T and suspect that the self-levelling rear is not working. To test I squeezed some fat lads into the boot then drove 'round a car park for a minute, but it didn't level itself. How quickly should the suspension react when you load it up?

The PAS works fine and the combined pump is not noisy. Also the damping seems fine at the back. What symptoms should I look for to confirm failure, or not?

Thanks for any help.