I had a leaking toilet and called Parker & Sons. Two "plumbers" showed up and after ten minutes let me know that my toilet needs a "major toilet tank rebuild". Cost $405.26 and since I used the company before a 10% discount was offered. Their reasoning was that because I had a bleach tablet in the tank, it totally destroyed everything inside. As I knew that a complete toilet is about $220, I declined the service. Instead I went to Central Arizona Supply and asked them for advise. After telling them that the toilet leaks into the bowl, they concluded that all a need is to replace the rubber at the opening. They told me that all I have to do give the chamber a quarter turn, take it out and replace the rubber. I purchased a package of three in different sizes. Cost was $6.30.
I went home flushed the water out of the tank, gave the part a quarter turn and took it out. The rubber showed no deterioration from the bleach. I noticed that the rubber had slipped a little over the rim, leaving a slight gap that allowed a little water to get through. I pushed the rubber back in its proper place and put the part back on. I filled the tank and was moderately comfortable that it would work. It is now six days later and I have no more leaking water. In summary, a trip to Central Arizona Supply and 15 minutes of my time saved me, after the discount, $364.44. I still wonder if they took the part out and looked at it.