Bought my 400E in January 1998. FWIW, here's the service history for the front brake pads. By the way, my 1993 takes 1992 front pads:

90,200
101,488
112,900
129,289
148,500
166,763
179,607
195,075
210,493
228,947

I think it averages about 15,000-18,000 per change. I noticed that it has increased as I age and my driving habits have changed. I tried the non-factory pads initially (Performance Products), but they only lasted about 5,000 miles. I have consistently used only factory pads since. I change the rotors about every third or fourth pad change. Maybe one or two good hard stops could have contributed to your increased wear.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles