Hi,
I've got a 1989 W124 300E that I only drive once a week or thereabouts. Recently (at least the last 4 or 5 months) the batttery has been fairly flat when I come back - certainly too flat to start it. It's a new battery (about 3 months old) because I had the problem and thought it was a battery issue. Probably not now.
I've put an ammeter across all the fuse positions (with the fuses removed) and the only current of any significance is Fuse 9 which has the interior lights etc. It shows about 0.35A. Apart from the radio and clock, I don't think there should be any drain. Is this too much for them? Should this be enough to flatten the battery in a week - 7 x 24 x .35 = 58 amp hours - sounds a lot less than should trouble the battery to me, but I may be wrong.
What else should I look for?