Noob here.
I just bought a used 01 S500 without any extended warranty. Recently, the automatic trunk open/close system no longer works from either the remote, the trunk button on the door (red led no longer on), or the red trunk button. Pressing either the door trunk or remote just unlocks the trunk without any movement up or down. BTW i have tried holding the buttons for 5 seconds. i have already check/remove/reinstall all the fuses which are 13, 57 and 62 (which i know by heart now) and they are fine. The door/trunk close assist (pulling the lid/door in tightly) still work fine for the trunk and the other 4 doors.

Please help before I have to resort to the stealership.

 

I have something similar on my CLS. The red button is lit up but does nothing when you push it. You can close the boot from inside the car but not from the boot end. Did you have any luck with your problem?