Brian,"sealed for life" is an often misunderstood term.
I believe that it refers to the Manufacturers production life of the vehicle in question which is often 5 or 7 years before the new model is introduced.
This will equate to 60,000 or 80,000 miles typically at an average annual mileage of 12,000 miles.
It does not refer to the life of the vehicle from an owners perspective.