ABS/stability control failure

My car has 49,000 miles and has developed an intermittent failure of the ABS/stability control system. The indicator reads "stability control failure" and the ABS symbol also illuminates. The failure tends to occur after the car has been driven on a hot day, then stopped for about one-half hour, parked in the sun, and restarted. Once the failure occurs during a day, it tends to remain for the rest of the day (but not always). The failure always resets overnight and never occurs when the car is first started in the morning. We got the car to the dealer once when the failure was occurring (because ABS codes are not stored in the ECM), and they said the ABS code indicated failure of the ABS module ($1,300.00). This code can also indicate failure of the ABS unit $1,600.00). The service adviser noted that the ABS module can become "confused" and to recommended we ignore the failure as long as it resets overnight. I have tested the ABS unit (in the rain) and it works just fine. I have inspected and cleaned the four ABS wheel sensors. I am guessing an intermittent of some sort in the ABS module. Any ideas?