Rheological Selling Point?

I took my 10 year old car (130,000 miles) in for an oil change recently.  The manager tried to sell me the high mileage oil, telling me "it expands to fill the cracks in older engines."  I turned him down, as I am an aficianado of NPR's Car Talk, and the two guys on that show have said that those products are a waste of money.  (The high mileage oil would have added $20 to my bill.)