Hi had simerlar prob few yrs ago, turned out to be the hyd pump/motor, get your to merc and have the fault codes read on the star machine, if it is the hyd pump/motor get them to check the pump/motor control, located under the drivers seat, as it was the control that had failed causing the motor to burn out, but dealer only changed motor/pump and three weeks later it happened again.
Darren Brown
December 2010