PT chance will get a boost if CSJ announced his retirement from politics. There are still voters hesitate to vote any SDP candidate as long as CSJ is there.
Plus the fact 5 years ago Liang Eng Hwa wasn't the incumbent. If he done a good job at local level and can connect with the heartlanders, then it going to be a factor that go against PT.
But at national level, PAP is experiencing a headwind. Very hard to predict here.