03 4 runner - VSC Light?

My friend bought a 2003 4 runner with a v8 and he loves it. He recently had the following lights come on - VSC Trac, VSC off, Brake, and ABS - plus his brakes seem like they don't work as well when this happens. He took it to the toyota dealer and they said that it was a bad wheel speed sensor. Replaced the sensor, problem came back, said it was a leaking seal on the rear axel causing the sensor to read bad. They replace the seal, my friend takes it home, drives it for a day or two - the lights come back on and this time they say it is the $2000 ABS computer. They replace that and the same thing happens. Sounds to me like they are just throwing parts at it. I am a mechanical engineer with a hobby of working on cars. I told him to take it to them because they have the specific computer to read the codes this car can throw, plus I didn't want to void his warrenty by looking at it - I don't think they know their butt from a hole in the ground. My question is this, does anyone know of a common problem that can cause all of these symptoms - and what can I tell the dealer?

Thanks, Jason