How to stop water running and flush without trouble, (Mansfeild #160)?

Our home is just seven years old and within the last twelve to eighteen months the toilet in the master bath continues to run. I've tried slightly bending the rod of the bulb and it will work for just a couple of days. I also have two toilets that are hard to flush, (all of my toilets are Mansfeild #160's). I have to lift the tank cover and pull the plastic arm in order to flush and that takes much pressure to do, in fact I broke one in 2007.