Complex sentence: Even with the sale of 50% of its shares to Silvio Santos in 1972, Record didn't manage to regain the lost ratings; the formation of SBT in 1981 marked the deepening of Record's decline.
Split into simpler sentences: Even with the sale of 50% of its shares to Silvio Santos in 1972, Record didn't manage to regain the lost ratings. The formation of SBT in 1981 marked the deepening of Record's decline.