If you move the headrest switch in the UP direction to you hear or feel the motor engage? If you do , the motor, gear, rack et al is good. The switch on the door needs to be cleaned. However if you are not handy you may want to buy a new switch. However they are cleanable and repairable. Soot builds up on the contacts and they don't make contact.

There is a documented process on this web page to clean and service Mercedes switches. The Door switches are a little more complex becuase they have more moving parts , but the DIY article explains it very well. I just had to fix my daughters seat swiches in her 86 190e and they work great again. These are the original switches, etc..