 Jack Brabham used BT19 again at the Italian Grand Prix at Monza , another high speed circuit . A second BT20 was completed at the Italian track and Brabham tried it in practice for the race , but decided to race his Old Nail , which he felt was fitted with a stronger engine . As at Reims , Brabham successfully slipstreamed the race leaders early on , but an oil leakage stopped the car after 8 laps . Neither Surtees nor Stewart finished the race and Brabham clinched his third world championship . 
