My wife recently went through the car wash with her radio on, leaving the antenna up on our E320 and it was bent. Do I need to replace the whole antenna mechanism or just the mast? Is this something I can generally find as a used item in the “Parts” “Classified” section and if so, what exactly am I looking for?

You probably just need a new mast. It comes with a long plastic leader which feeds into the motor. Unscrew the top nut on the antenna mast, raise the antenna as much as possible, pull out the old mast gently, insert the plastic leader until it grounds out on the intake reel, lower the mast or turn the radio off. It should feed in properly. Then tighten up the nut. At least this is the way it works on my 300SD. Piece of cake. Look in the forum parts for the mast.