Complex sentence: Thus the factory's David Brown Racing Department would no longer compete in sportscars, leaving the four DBR1s retained by the factory, including the rebuilt DBR1/3, were sold off to customers for use in various championships.
Split into simpler sentences: Thus the factory's David Brown Racing Department would no longer compete in sportscars. The four DBR1s retained by the factory, including the rebuilt DBR1/3, were sold off to customers for use in various championships.