I strongly recommends you have the dealer check out the actual car that you
have decided to purchase before you actually buy it.
Yes, the self levelling system is a major issue because these cars does not
have any springs for suspension nor sway bars... it actually relies on the
computer to compensate via hydraulic and gyroscope.
The suspension/steering pump is a ton of money and so are each of the
hydraulic unit at each corner...
Most common issue is the hydraulic hoses are weeping... simply grab the
hoses if you can... if it is soaking, then those hoses needs to be rebuilt
with new hoses and crimped by hydraulic hose shop... or if you want to spend
a fortune... buy new hoses from dealer.
Let the dealer plug in the computer and do all the diagnostic tests... the
computer are really detailed on condition of the system... particularly the
suspension system. and everything else on the car.
Best to get the full service records too.