Ignition/starter problem

I have a 2001 Cadillac DHS; I am the original owner. A few years ago, I had a problem with the ignition lock which would not activate the
starter when turned to the "start" position. The dash lights came on with the first position, but nothing happened when I turned the key to "start".
This was an intermittent problem at first, and repeated attempts to start the engine usually resulted in starting on the second or third try. Finally, it became impossible to start the car and I had it towed to the dealership, where it was fixed under warranty.
Now, the same problem has re-surfaced. The vehicle has 117K miles on it and the transmission was replaced about 7K miles ago. The car has been running well with no other problems and the battery appears to be healthy (replaced about a year ago).
Does anyone have any ideas as to the cause of the ignition probem? I have found a number of similar issues on some of the websites, but no one is clear about the *cause*. Does anyone know of a recall or other Technical Bulletin issued by Cadillac which might help me get some financial assistance in getting this situation repaired, as it seems to be a systems problem with Cadillacs of this vintage.
Many thanks,
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