You don't need to use what your dealer uses - there is zero logic in going out of your way to obtain one oil over another. Did they tell you that they did, or do you simply think that they're on to something?
I would go with a synthetic 5w20 like Pennzoil Platinum. If your really hung up on a semi sym make your own with a 50/50 blend of PP and PYB if you can't find Pennzoil Gold.