That's good to know. Any leads on parts sources

Sure but you won't be able to find anyone willing to rebuild it the labor cost would be more than two by the unit out right that's why they do that. Look around I'm sure you can find the parts also

I can confirm that the price on the PTU complete unit has dropped fairly considerable compared to a couple years ago,this is what my dealer informed me after having my PTU Flushed,not sure if this is related to the plant in Mexico.  Z

Hey Grey....  Sorry, I just read this post.  So, I had this happen to me as well in my flex once.  I was worried.  Was messing around on the street doing multiple boost launches and then suddenly just blowing off the front tires like crazy.  I thought it was a fluke so I was coming out of a turn and got on it and just smoked the front tires at half throttle.  It has only happened the one time.  Haven't had a problem since.  So I would say its most likely a heat issue that stops the rear from engaging.  I don't think this is anything to worry about to be honest.  I was at first but not anymore.

So is it from a hot trans, rdu, etc.?

It has happened to me a few times and after the Flex cools it goes away.

Trans temps are usually around 205 when it happens... coolant is at 180 degrees.

Unfortunately, the PID's for AWD on/off and modulation are not loaded on my computer.
With these I would be able to see if the signal is being sent to the RDU.

I don't wasn't to visit the dealer to add them.. I would have to tear off all the mods.