Both of my toilets have had flushing problems for about a year. Sometimes you press the lever and nothing happens, other times the toilet runs & runs & runs without stopping. I figured out some time ago that the flapper chains were falling off the levers and either sitting at the bottom of the tank or (worse) getting stuck under the flapper. Solution? Take the lid off the tank and fish the chain out. Repeat as needed (typically at least once daily).
When you see how easy it was to fix this problem, you will be amazed that I spent a year plunging my hand into an icy cold toilet tank. I guess I'm just that lazy.
How to Replace Your Toilet Lever
Step 1: Gather materials and remove lid from tank.
Step 2: Stand by for inspection of Step 1.
Step 3: Loosen nut on inside of tank and remove handle/lever assembly.
Step 4: Stand by for inspection of Step 3.
Step 5: Remove hook from corroded lever.
Step 6: Stand by for assistance with Step 5.
Step 7: Install new lever, attach chain.
Step 8: Replace lid and admire.
Total repair time (including inspections): 10 minutes.