Here is a description of removing a 300E door panel from another post on this site:
Remove Door Lock button.
Open door and remove about two screws that secure the back plastic shroud around the door striker.
If applicable remove speaker grill (I don't think youreally need to do this, but again, I'm going from memory and my car is not here. Btter to remove and look around for fasteners. For front doors, this is N/A.
This is the tricky part - there is one more screw behind the inside door release handle. The black plastic shroud has to be slipped forward before it comes off to reveal the screw.
I don't know if the seat switch comes off wioth the pael, but my guess is yes, since there is no access to the back side until the door panel is off.
Noe the door panel is free to remove. There are about 8 or so "L" shaped clips around the panel and on the door pull, these slip thru slots on the door frame and then down to secure the panel. So to remove, you must slide up to disengage. My panel was very reluctant to come off, since this it probably had been untouched for over ten years.
Disconnect the speaker wire and set the panel aside.
There is a thin sheet of pastic that is glued to the door frame as a moisture barrier. If you work it slowly, you can probably get it off without ripping it.
Reverse the steps to reassemble and I would suggest an extra set of hands to help push the panel against the door so all the L brackets engage. It took me a couple of trys!
taking off the door panel