I just purchased my first Mercedes, a 1982 280E imported from Germany. Can anyone provide some tips for fixing/replacing a stuck antenna? The car has the original Becker Autoradio; should the antenna raise and lower with power on or off?

Also, the door locks do not operate well manually, and the owner's manual suggests that they are part of a "Central Interlock System". How do I go about getting these to work properly?

Thanks for any and all help with these issues.