Complex sentence: Since its introduction in 1963, Sisil was the leading refrigerator brand in the Sri Lankan market; this continued until the 1990s, when Sisil lost its position to increasing number of competitive brands.
Split into simpler sentences: Since its introduction in 1963, Sisil was leading refrigerator brand in Sri Lankan market until 1990s. But in 1990s Sisil lost its position to increasing number of competitive brands.