Mansfield toilets with a plunger style flush valve requires a Longer than normal Flush Handle. The original flush handle is plastic so if it doesn’t rest in the center of the hoop on the plunger it can cause the tank to leak wasting water.
A small amount of heat will soften the plastic so it can be bent so it does not put sideways pressure on the plunger.
An after market flush handle made of brass is easily bent (outside of the tank) so it rests in the center of the hoop.