I think my last post was appropriately deleted for having implied that Main Sail/SickCat... well, i wasn't very nice. I was right, but clearly inappropriate.
People, if you have questions about engine manufacturers approving of synthetic oil use, go to their sites and look. No seriously, go look. See what they say. Granted, in the case of a 1GM, it will specify API CD, an old standard mineral oil, but you will find there is a Synthetic which is hands down a better choice than standard mineral oil. Same standard, only better. Many of them offer their own brand of full synthetic (CAT, Yanmar, Penta, Mercury,etc..) or at the least, specify the API Standard to which your oil choice must belong. Finding that, you should visit the API Standards website and locate the synthetic which meets and exceeds the engine manufacturers recommendations. Unless you are educationally equipped to dismiss facts of a field you are not educated in (i assure you i am not), and you are interested in exploring the benefits of this type of upgrade, perhaps listen to qualified and current sources. I have nothing to gain, other than the respect of my customers who opt to try it. I do not put their engines at risk because the lubes i use exceed those required and are the same which come in all their latest engines, and although some decide that the change frequencies should remain the same, they still appreciate the protection the oil provide for their beloved investment.