Regarding the 380 question.
This reply is not so much about mpg, but a word of caution.
I may stand corrected on the year, but I believe the '84 model was refitted with a double-row timing chain. Earlier models had a single-row timing chain and these were known to fail.
Check thru the archives here to ensure I'm right about the year MB switched to a double-row timing chain. I you find a 380 you like, make sure it's equipped with such.
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.