1996 Honda Accord What can I do?

It all depends on how it was treated the first 250,000 mile's how long it might go after. If it wasn't maintained the first 250,000 mile's then there is nothing you can do to reverse that damage. But 500,000 mile's is wishful on that car or most car's. If you want a car that might last that long but no telling that it will your looking at a well maintained diesel like a Mercedes Benz or something like that. Buying a car with that kind of mileage and expecting to get many year's and a quarter million mile's more out of it is not a good plan. If I had the answer you were looking for I would make a lot of money selling it in a bottle.