Brake Antilock Wheel Speed Sensor problems of the 2009 Ford Ranger

My parents 2009 Ford Ranger has had an ongoing issue with the brakes. We took it to the local Ford dealership and they diagnosed the problem as a wheel speed sensor was not working. They installed it and it didn't resolve the problem! on day two, they came up with a new diagnosis that the tone/exciter ring was damaged by a previous mechanic/brake job. The truck has less than 35,000 miles. They wanted another $400 to replace the tone ring. I declined because it was way too much money after paying $300 for the sensor. They said they couldn't warranty their work, afterwards, I began to research Ford brake issues, and specifically abs & tone ring issues. It turns out, that after looking at various youtube videos, Ford forumns, articles, etc. I learned that Ford has had significant abs issues especially in 2008 and 2009. Even more interesting was the fact that many models have had the same problems (focus and escape) and have may have been recalled. Not 100% sure, but the Ranger has not. Basically, the tone ring is attached to the wheel hub/axle and spins with the tire. This creates a magnetic field wherein the sensor determines the speed of the wheel. If the tone ring is damaged, the sensor sends various error codes to the ecm at which point the abs brake will disengage the brakes on the wheel affected. And then it will engage the brakes, and repeat this until the vehicle comes to a stop. Essentially, the abs system overrides the break pedal and you lose braking ability on that wheel. Not only that, with my vehicle, the abs warning lights have never come on; even after they replaced the sensor. The vehicle is getting worse. At every stop it's making noises and it's harder to stop the vehicle. As I said earlier, the theory is the corrosion of the axle is breaking the ring, which is another non rusting metal, I'm pretty sure the dealership did not examine the ring. Help!!!!.