Complex sentence: Whilst Labor had held Rockdale at all times since the district's re-creation in 1941, it only barely retained the seat at the by-election; the party suffered a large drop in its vote compared with the 1984 state election.
Split into simpler sentences: Whilst Labor had held Rockdale at all times since the district's re-creation in 1941, it only barely retained the seat at the by-election. Labor suffered a large drop in its vote compared with the 1984 state election.