Are High Mileage engine oils beneficial

Are "High Mileage" engine oils beneficial?

Are "High Mileage" engine oils really beneficial to high mileage engines? Would full synthetic still be the better choice?

Other Answers:

If your high mileage engine smokes on startup, a blended hi-mile oil has detergents and chemicals that soften and (swell) old seals and MAY help in stopping valve seal leaks.
If it doesn't smoke, a good synthetic will help with friction, especially the rings.

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High mileage oil has more detergent. If you change your oil, you don't really need it.