Why do you need to turn the rotors?
Also, did your mechanic use brake pad paste as recommended? I had a little squeal in my front brakes after I installed the "green stuff" pads from EBC on my wagon. I pulled the pads out, used the brake pad paste as recommended by MBZ, reinstalled the pads, and squeal was gone.
OEM pads are very good. Only drawback in my opinion is the prodigious production of brake dust. If you can live with the dust then OEM is certainly a way to go.
Does Brembo recommend a specific type of pad for use with their rotor, such as metallic or semi-metallic? I've got Axxis metalmaster pads on my wife's 300E and they work fine, don't squeal, and don't make much dust.
Hope this helps
92 300E (Black/Grey interior: wife's car)
94 E320 Wagon (White/Saddle interior, Eibach springs, '96 E420 16 x 7.5 wheels)