Brake Sensor problems of the 2004 Chevrolet Express

My anti-lock brakes activate at low speeds. We first noticed it around 37,000 miles, but now it occurs almost every time we apply the brakes at low speed at 39,000 miles. We discussed the problem with two chevy garages - both admitted that it was a common, known corrosion problem that requires either cleaning the brake sensors for approximately $200 or replacing them at a cost of approximately $460. This is a huge safety issue for us. The van drifts forward too far when we stop and we are concerned that we will either hit another car or possibly a pedestrian. We are concerned that this will be an ongoing problem with the vehicle as we are located in new york state and salt is a common winter corrosive.