Mobil 1 is an excellent synthetic, it's the featured oil for Mercedes Benz, says so right under the hood. For BMW, it's Castrol Syntec, not as good, but a good lubricant nonetheless. And I think that's what comes in Cadillac and Corvette.
I used Mobil1 for many years when it was hard to get Amsoil. Once they got an online site and shipping to your door I went back. Plus, as mentioned, they have a product for virtually every application. So you don't have to hunt around for a satisfactory synthetic for something special, like for example, outboard motors! What's interesting to note is that all of the major oil labels pooh-poohed synthetics, saying 'oh, you don't need that' and now they all have their own synthetic or semi-synthetic products.
You can switch any time without a worry. The only time it's not recommend is for something that is at the end of it's useful life and the gum and sludge is what's holding it together. Like a card with 150K or more on the clock. The synthetic will clean out all that crap and plug a filter or cause oil consumption since there's nothing in the ring grooves to stop the blow-by.
For your outboards it's not a problem to swtich. Get the lowerend lube too and just switch the whole thing when you service them.
Let me know if you want to get setup to buy direct. I would appreciate any referals from fellow Grady enthusiasts.
