I understand that you have leveling capability on all 4 wheels. Normally, our USA version will have the leveling feature on the rear only. However you still might want to check this site for a basic pressure test of your hydropneumatic leveling sys. It might help you spot leaks.
http://mb.braingears.com/126_DISC2/program/Chassis/32-530.pdf
Brgds,
BENZSTER