It can be the switch or the control unit. To test this you will have to connect a meter to the seat switch and get it to fail. If the switch is sending a signal to operate the seat ny mistake it is the switch. If not look at the control unit.

------------------
Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM