Complex sentence: After a difficult year with Ferrari in 1973, he moved to Williams and finished third in a non-Championship race in Brazil, but the Championship seasons of 1974 and 1975 proved largely unsuccessful, but he finished fourth in his home Grand Prix at Monza in 1974.
Split into simpler sentences: After a difficult year with Ferrari in 1973, he moved to Williams and finished third in a non-Championship race in Brazil, but the Championship seasons of 1974 and 1975 proved largely unsuccessful. However, he finished fourth in his home Grand Prix at Monza in 1974.