I recently went to open my trunk and found that the trunk opened but the trunk lid motor kept running without the latch moving back to the fully raised position. My first instinct was to buy a replacement motor. But upon inspection, it appeared the entire motor assembly was fairly easy to remove (three bolts and disconnect one electrical harness and out it came). Now that I could put it on my workbench, it looked simple enough to break down to determine the problem. A couple more bolts and I could inspect the internal gears.
Once disassembled, I noticed the teeth on the old plastic gear were worn to a point where they no longer meshed with the motor worm drive. I went on Amazon and found a new gear that was a perfect replacement to the original. But, before the new gear could be threaded on the trunk latch I needed to use a triangular metal file to cut those metal trunk latch threads back to near original condition. Apparently, not only were the threads on the old (plastic) gear worn, but the metal threads on the trunk latch were also worn (rounded). Once I did so, the new gear threaded beautifully on to the latch and traveled up and down the shaft without resistance. Reinstalled the unit and it worked like new. Got a quote for sending this out for repair $115 plus postage (another $20). Did it myself and gear cost $15. Not a bad return for my inquisitive nature. Difficulty of project 1=easy 5=very difficult... 2 (would have been a 1 if it weren't for having to file those metal threads).
Cool story. I was worried your issue was going to be the switch and the failed ones I have encountered were not repairable or easy to find replacements. As you found out the mechanical bits are not that hard to find. There were some other GM cars that used the same mechanism so its not a Cad only item which I think helps.