Make sure the anti-squeal shims are properly installed, and that the retainer pins and springs are in good shape.
Disk brakes squeal a lot -- MBs aren't too bad, but volvo 740's are notorious for shrieking brakes -- a friend of mine worked for NATO in Belgium, and the border guard would put their fingers in their ears when he drove up in his 740 it squealed so bad.
Soft pads help, as does gentle braking until the squeal goes away -- if the pads vibrate a lot, they can wear funny. MB OEM pads are relatively soft for just this reason -- very good braking and no squeal. The price is short life.
I'd recommend gentle braking and coasting down to stops anyway. I love to drive fast, even in the old 72, but my brakes last forever -- 60,000 in the Volvo front pads, at least 20.000 on the 220, etc. Gentle stops are easier on your passengers and the rest of the car, too! Probably a habit left over from my first car, a 1962 Oldsmobile Dynamic 88 -- ran like a bat out of hell -- easy to run 90+ on the highway without knowing it, and brakes smaller than our 1970 Bettle...... one learned to brake early and often, or one didn't stop at all --- you could lock up the tires, but still didn't stop very quickly! Ran amny a stop sign, passed many a driveway until I learned to slow down early.
The MB recommendation is a set of rotors each third pad replacement. My mechanic replaces rotors if there is a discernable lip on the outer edge -- when they are worn enough to show this ridge where the pads don't cover the outer rim, they are too thin to machine. Never allow them to get too thin, as the pads will run up on the retaining spring -- this will cock the piston in the bore, cause the brakes to drag badly, and bake the rubber parts, ruining the caliper..... exspensive!
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!