This question has come up before, and it appears as if the answer is still the same as the last time--which isn't a revelation as it has changed over the years. I think some of this can be found in a thread called Mobil 1 or something similar.
The correct Mobil 1 to use in our older engines is the one formulated for such, which is their 15W-50 with the SILVER cap:
http://www.mobiloil.com/USA-English/MotorOil/Oils/Mobil_1_15W-50_.aspxThere was an issue a few years ago, where the consortium of engine remanufacturers got together and pooled their knowledge and were finding that there was a "above average" number of remanufactured older engines failiing prematurely. When they all got together and discussed it the culprit turned out to be modern oils without ZDDP in older engine designs. (Note this was not specific to Mobil 1; but the absense of this lubricant in the oils used in the remanufactured engines).
I think that regardless of who manufactures the oil, there are limiits courtesy of our Federal government on the amount of ZDDP and Phosphorus and other compounds in the oil. They would hold true for any oil, though. I also believe there are extra-wear additives that you can add to oil. There's a lot of information available on the subject on the internet, not surprisingly concentrated in Corvette (older but high performing engines) and Triumph (older and ancient design) forums! The debate rages on and changes with each engine breakdown (looking for a culprit) and with each oil reformulation.
Long story short, there was a short period of time when NO Mobil 1 product had the proper lubricant for older engines; it has since been reformulated and the link above is the product. FINDING it, however, isn't always easy: you may need to mail order or special order it. It is not always on the shelf of local auto parts stores. The naysayers claim that Mobil's discussion of the product are vague.
The other issue with synthetics in general (again, not limited specifically to Mobil 1) is the claim that when people put it in, all kinds of leaks happen. I called Mobil on this and their claim is that it does not
cause leaks, but if you
have leaks, albeit small and controlled leaks that are common on say, a 40+ year old engine that has not been rebuilt, the use of synthetics may indeed exacerbate them.
I started using Mobil 1 the moment my engine came back from Metric nearly 10 years ago. I don't have any leaks to speak of; it didn't cause any in a freshly rebuilt engine. Others here on the forum with non-rebuilt engines who switched to synthetics suddenly discovered all kinds of leaks. I don't have an overdrive; I don't have a 5-speed; I don't have a modified or replaced rear axle, it is "as delivered" and the car is running 4,000 RPM at highway speeds. About 13,000 miles since rebuild, no apparent issues yet.
Use what works for you. My local mechanics generally use the diesel class Rotella in older engines, as do lots of vintage Mercedes users. The more research you do the more contradictory information you'll find. Nothing like gray area to clear it all up!
