i would replace the the temperature control unit, the one in my car was bad and the ac wouldn't turn on or adjust and then secondly when the ac system starts to run low the air can get so cold that it will freeze which means you probably have a slow leak somewhere, about the tranny my car does the same thing i just kinda ignore it theres a way to adjust it but i have had 2 previous Mercedes that would kinda slam into gear and then i had a Mercedes that would always shift in perfectly i forget how to adjust it but its somewhere on the side of the thing, I remember on my 300SD the reverse gear went out and i thought the transmission was screwed then i found out it was just a bolt for the reverse bolt was loose after that it worked perfectly. As long as the thing shifts right you don't have anything to worry about. for the vibration you may want to replace the tranny mount which is right where it connects to the drive line i did that and it made a diffrence for me. good luck with the car