Welcome!
Mr. Frugal may want to consider used for his headlight bits.
Try
http://www.uneedapart.com
Junkyards bid for your business!
Unbelievable price deviations come back.
I have had good luck with this service.
Sometimes you can manipulate the headrest while pressing the down switch, if it has gone "off track". Worked for me.
Listen for the motors trying to operate. If they are not even making the attempt, it may be the switch itself. This requires poking at it with a multi-meter to diagnose.
If the motor is kicking in, but the seat is not sliding, it may just need a 'clean and lube' on the tracks to unstick it.
Best of luck with your 'new' 124.