Saturn & synthetic oil?

First pardon me for cross-posting. It is not meant to irk anyone but to ask as many people knowledgeable about GM cars as possible. When I recently purchased my 2007 Saturn ION 2, the first thing I asked the
service people is when can I switch to syntetic oil. They recommend waiting until at least 10-15,000 kms to make the switch and use ONLY Mobil 1. Just as if other companies don't make good quality synthetic oil. Sheesh!. But I can live with that. Mobil 1 is excellent stuff. What makes me perplexe is when they said not to use synthetic in the standard transmission. I don't understand their reasons why. So, is there anyone out there who can explain why I shouldn't use synthetic gear lube? Thanks
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snip

Thanks for the info.
Snip

Are you absolutely, positively sure the oil caused the failure? I have used Amsoil for many years and have had great results in my cars, motorcycles and lawnmowers. I know other people who rave about it too. In the early years, (early 70's), seals shrunk with Amsoil but seal swelling agents solved the problem. I think Mobil 1 was causing the same problems but I am not 100% sure. Police fleets, trucks fleets, racers, etc, use Amsoil and other synthetic oils with good results. Did you have an oil analysis done to prove it was the cause of the main bearing failure?
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Had to be the oil, racing does not wear engines very much. I'd guess a typical NASCAR or USAC engine can go 100k with no problem as long as they do the required oil changes.
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