Can you email me some larger pics bro? Close-ups if possible, and include all your repairs. Looks simple enough (simple being relative to an actual inspection, of course) and should not be a problem to either tell you how to fix it or take a day and do it myself - and it will take a day, as I am forced to take many breaks to keep the swelling in the leg down.
Let me guess: your leak is about 2 feet above the window top, right? I cannot tell if that is an asthetic feature on the home or a sink (wet behind the exterior coating that sat and shrank the foam, making a gap that water found to invade your sheetrock inside).
You're telling us that no OSB exists on the exterior framing, but I think you are incorrect. I see no way of a home passing inspection without sheathing, followed by TyVek (a DuPont water and moisture barried used to seal the wood and attach the styro and chicken wire that makes the stucco or DryVit stick). More than likely, moisture entered between the TyVek and OSB and rotted a portion of the wood - as Rusty said, stucco is NOT waterproof, and is sealed only with latex paint on the exterior. If water or excess moisture enters from behind, the bonding process fails and the stucco will crumble.
I'll put dollars to doughnuts that's what happened, and caulking it doesn't stop the separation permanantly, which is why it works for a little while and then begins to leak again: the stucco is still crumbling, leaving nothing for the caulk to adhere to. It just falls away over time.
The correct fix will be to remove a larger portion than what is affected; replace the OSB; seal properly; new foam and wire; and, finally, stucco and paint. Again agreeing with Rusty, we should inspect the window seating while we are at it and replace anything suspicious. We'll also want to make damn sure no mold exists and, if it does, replace those areas as well. Once mold is prevalent it is almost impossible to be rid of and inhibit growth, so better to replace.
But I'll know more with better pictures. Send me outside closeups and pics from inside, too. Annotate where the leak occurs if you can.
And don't worry about doing anything more than I asked as far as compensation. I won't accept it, so you might as well save your breath. Beer and McD's and gas money is plenty for a fellow ARFCOMMER. If you want to say thank you, help someone else out without charge when you can. We AZ people need to stick together.