Complex sentence: Also that year Siddeley partnered with Walter Gordon Wilson, inventor of the pre-selector gearbox, to create Improved Gears Ltd, which later became Self-Changing Gears-the gearbox that should be credited with enabling the marketing tagline "Cars for the daughters of gentlemen".
Split into simpler sentences: Also that year Siddeley partnered with Walter Gordon Wilson, inventor of the pre-selector gearbox, to create Improved Gears Ltd, which later became Self-Changing Gears. The gearbox that should be credited with enabling the marketing tagline "Cars for the daughters of gentlemen".