We put Mobil 1 in a vehicle with over 400k miles. But the way we got the vehicle to 400k miles was changing oil and oil filter every 2500 miles. I did the same with the Mobil 1. We used the Mobil 1 from about mid November through the first of March when we switched back to Motorcraft. Did this for several years.
The reason: had to have one vehicle that would start in the winter months.
No leaks, don't know about fuel economy (but I doubt it would ever pay for itself). As to wear, how much more engine life can you ask for? The secret to long life engines is change the oil and filter.
When we retired the vehicle with almost 500k, the cylinder head had never been off.
Jon.
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"Good carburetion is fuelish hot air". 
"The most expensive carburetor is the wrong one given to you by your neighbor".
If you truly believe that "one size fits all" try walking a mile in your spouse's shoes!
Owner of The Carburetor Shop, LLC (of Missouri).
Current caretaker of the remains of Stromberg Caburetor, and custodian of the existing Carter and Kingston carburetor drawings.
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