GM-GMC: What type of Motor Oil is recommended for a 2000 Cadillac Escalade with a 350 engine, rear main oil seal, engine leaks

Question
I hope this question is within the realm of your expertise. I very recently purchased a 2000 Cadillac Escalade SUV with approx. 96,000 miles. I bought the vehicle from a cadillac dealer, in Owosso, MI. I have referred to the owner's manual, for the type of motor the manufacturer recommends using. This vehicle has the 350 engine, and 5w 30 or 10w 30 is what the owner's manual suggests using.

I have thought about using a synthetic oil such as Mobil 1, but have not been able to get a straight answer from the dealer whether it's okay to use synthetic in this particular engine, with 96,000 miles.

Do you have an opinion regarding my using synthetic oil? Is there any particular advantage, or perhaps you would recommend staying with an conventional all climate oil.

Lastly, do you recommend using any kind of additive at the time of an oil change?

Thank you for your help, and I look forward to hearing from you!

Dave Hinks  

Answer
Though not the type of question I normally handle, I will try to help.
The first question you need to ask is, "How long do I plan to keep this vehicle?"  The second is, "Are there any oil leaks or oil consumption problems with this engine?"
Given your location, synthetic oil is the best possible choice you could make for your engine's benefit.  Synthetic flows much better in very cold weather and is vastly superior in resisting oxidation in hot weather.
One of my Toyota MR2s has had synthetic oil in it for 100,000 miles.  It is just shy of 160,000 miles and it runs perfectly without using any oil.  I bought it from a former co-worker back in 2001 and he has used Mobil 1 for years in all kinds of vehicles.  One of them, an early 80's Chevy Citation V-6, I had the task to replace the rear main oil seal.  That was the cleanest engine I have ever seen except for my MR2 (when I replaced a leaking oil pan gasket).
If your engine leaks or uses oil, you will find that synthetic oil is VERY expensive.
There is no concern over compatibility.  Mobil 1 was modified years ago not to damage seals that have been run in conventional motor oil.
I would use Mobil 1 10W-30 in your climate.  It is readily available and that was is in my MR2, which has seen weather ranging from winters in Utah and New Mexico to summers in the desert of California.