I have had the same problem since I have owned my 97 4runner. The brakes get bad because the oil that leaks out fills the cylinder that pushes the shoes against the drum. They lock up and vibrate like hell from warping. A quick little fix is to loosen the automatic tensioner inside the brake drum. (The downside to this is that until they readjust which sometimes takes a while, the brake doesnt work. I have slotted/drilled front rotors to take up the extra load, since the stock ones are not up to par anyway.) You need a manual to understand how to do it, because I dont think it would be very easy to explain. It involves sticking two screwdrivers in the drum from the back of it. I have had 3 new sets of shoes/ drums, changed the seals many more than that, and even changed a supposed bent axle housing only to have the problem return. Too bad my baby isnt under warranty anymore. Some have suggested its the supercharger sending too much torque to the rear axle, and some say its from doing donuts. I now just loosen the tensioner every few months, which once you have some practice doing, takes 5minutes a wheel. Do you have the locking rear diff? I wonder if that has something to do with it. SOMEONE HELP US