IIRC, there had been lots of things wrong with Lefty's bird, which caused the crash. IIRC, he didn't take care of a lot of stuff with the engine, he just kind of flew it without thinking about it, and did just small modifications. (which IMHO, is amazing for a bird as old as that)
Get a clue his son was flying it when it crashed

An interview with Ladd Gardner - Introduction
reprinted from AAFO.COM
For many years, fans of air racing and air shows across the nation were treated to the unique experience of seeing Lefty Gardner fly his race modified Lockheed P-38 Lightning, known as "White Lightnin'" as a competitor and show performer.
On June 25, 2001, during a return flight to Texas, after appearing at an air show in Tullahoma, Tennessee, Lefty Gardner's son, Ladd, experienced an in-flight engine fire in "White Lightnin'" forcing him to put the airplane down in a field. Though the airplane was substantially damaged, Ladd was uninjured and the airplane is repairable...
Earlier this year, we spoke at length with Ladd about the accident and his life leading up to flying one of America's great aviation treasures.
Ladd's account of the accident, his life growing up in the aviation oriented Gardner family and his family's quest to gain the necessary funding to return "White Lightnin'" to flight status chronicle both his aviation career and what has become his life's goal.
Get "White Lightnin'" flying again.