After 100,000 miles, a range of repair needs can start to come up. You’ll want to watch out for breakdowns involving the drivetrain (engine, transmission, and drive axle). Sometimes you’ll just have to fix worn-out seals and gaskets. Transmissions may have to be replaced in less-reliable vehicles after 100,000 miles. In rare cases, you might have to replace the engine, which can cost up to $5,000 or more.