What is the secret to removing the caliper brackets and replacing the rotors on a 1991 Euro?

A good metric socket set, penetrating oil, and a big hammer. Actually, an impact wrench is the key. Keep in mind that the caliper itself is held on by 2 bolts to the caliper bracket. And the bracket is held to the car by 2 other (I think larger) bolts. The 2 that hold the calipers to the brackets are loosened every time you change pads and therefore are usually not as hard to remove as the 2 that hold the bracket to the car. Not only that, but these 2 bolts have what look like washers on them but these "washers" are actually part of the nut. This gives them a large "friction" area. And this friction area has ridges or grooves on it so as to sort of "embed" themselves to whatever they tighten up against. So don't try removing them with steady pressure, but rather a "beating" motion. An impact wrench would be ideal. You will require a 15mm socket or wrench for the caliper slider bolts, and a T60 torx for the bracket If your doing the rear you will need 18mm wrench