By this time if they haven't had a valve job they need one. Have the car checked over by a competent tech who know Mercedes. The transmission should be payed attention to and the service records looked at for the trans service. If these things are in order, you should be fine. And check the A/C.
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM