If you disconnect / reconnect the negative terminal on the battery, is there a large spark?

If so, you might have to try troubleshooting your drain by pulling fuses and seeing if it lessens or goes away (a multimeter will help greatly).

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1982 240D, sold 9/17/2008
1987 300D TurboW124.133 - 603.960, 722.317 - Smoke Silver Metallic / Medium Red (702/177), acquired 8/15/2009
262,715 and counting