Is that an American Standard Champion 4? I guess its bigger area causes more pull to be required.
Can you adjust your lever arm to lift more straight up? I think that may reduce the resistance. Also, I was thinking that maybe you could increase the slack on the chain so that the lever would hit the tank lid just before the green thing hits its stop. That way, the tank lid would serve as a stop rather than having the force carried by the chain. Alternatively, maybe glue an appropriately sized block to the underside of the lid to serve as a stop.
Could it be that one of the users likes to use his foot to flush. Is it the case that it never broke when you flushed, but it happened when somebody else uses the toilet? I wonder if each time that when the chain breaks, the toilet flushes one last time, or whether the chain breaks before the green thing lifts, giving no last flush.
If you decide it is some user(s) who are too vigorous, as opposed to the green thing taking too much force to lift, you could consider installing the Kohler Touchless Toilet Flush Kit. That way, the person who does not want to touch the handle with his hand could meet his objective. If the tower is simply taking too much force to lift, then that would not help.
Another idea: rotate the lever so that the user must lift to flush, rather than push down. He might still use his foot, but he will not be putting his weight on the handle.
