You do not have to coat the gaskets. I'm not familiar with steel plates that would get in the way of pan removal. Perhaps someone else familiar with the 380 will respond to this issue.
Don't forget to drain the converter. It's forward of the pan and holds as much or more fluid than the pan. In my case(also a 126 car), it's covered by a U-shaped cross member that has 3 bolts holding each side in place. I believe a 17mm socket gets them out.
1991 300-SEL - Model 126
M103 - SOHC
James Madison - Oppressors can tyrannize only when they achieve a standing army, an enslaved press, and a disarmed populace.
Liberty Firearms Training - After years of trying to regulate California criminals with a never ending stream of gun control laws they have still not given up with the belief that if they make something a crime that criminals will miraculously start obeying the law.