It's my understanding that the part that plugs into the injectors (we'll call it the "harness") is the part that has been updated to lock into the other part (call it the "gasket") and prevent it from shorting out.
Mine has done this twice and each time it was just a loose connection. First time I rigged it, second time I replaced the "harness" and it has been fine since.
As RacerX mentioned though, sometimes the bad connection causes damage to BOTH parts making it necessary to replace them.
At any rate, try to get your parts from an International dealer if possible, or if you can wait you can go thru powerstrokeshop.com I say this because if you go to Ford, prepare to be raped.
The "harness" part I had to buy was $18 from International. Guess how much from Ford...
The "gasket" part of the deal should be around 30 bucks as well, so less than 100 in parts even if you need all of it, provided you get a fair deal.
My symptoms were exactly like yours, it would fix itself for a day or two, then one day it died and would NOT start back. Finally got it started and it had no power and ran like poo because it was only running on one bank.
The OBS connectors are split into 2's, so you only lose 2 at a time normally if it's the "harness".
Your situation sounds like it may be the "gasket" part as RacerX mentioned, and that's why it won't start, only one bank trying to light.