The 10k oil synthetic oil changes wouldn't have caused that engine to lock up unless someone forgot to replace the oil plug. Something else failed for the engine to die that prematurely.
I ran into a guy years ago who had a Nissan Sentra with 450,000 miles on the odometer. It ran like a top and didn't smoke at all. I remarked that he must keep his oil changed very regularly. His reply? "I used to change it every 5,000 miles. At 175,000 miles, I realized I could replace the engine with a junkyard motor for less than I was spending on oil changes. So since then, it's been changed every 15,000 miles with conventional oil. Of course, I'm on my 4th junkyard transmission...". It was an eye-opening discussion.
One thing's for sure, changing your oil every 3k won't hurt anything other than your wallet....
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His engine locked up because the dirty oil caused scarring and the oil journals were clogged enough to cause insufficient oil flow. Doesn't take much grit / dirt in the tighter tolerances in newer modern engines. The dealership and the rep from G M are the ones who diagnosed it. Dealership did every oil change from day one. $30.00 every 3 or 4 months doesn't hurt my wallet too much. Like I said. The peace of mind makes it more than worth it. I do all my own maintenance and repairs and I enjoy doing it.