Transfer Case won't engage

My 2000 Ford F250 Super Duty won't engage the front drive axle when I shift (ESOF) from 2WD to either 4High or 4Low. The drive motor on the transfer case will run (it cycles three times and quits) but nothing happens? The front axle will not engage. The motor is V10. The hubs are set to auto. The 4X4 light on the dash only lights during the test sequence when starting the truck. I'm the original owner and have used the 4X4 extensively until now. I had some diagnostic work done at Ford dealer and indications are the drive motor on the transfer case, but they were not real definitive. Since it is a $500+ dealer only part I was hoping for some other suggestions or alternatives?