Frankly, I don't have a clue as to why your old toilet isn't flushing as it should. Now I realize that spending another persons money is quite easy, but here's goes anyway. That old toilet even if repaired and operating is wasting at least 1.5 gallons of water every flush and perhaps even more depending on its age. Many areas offer a rebate for replacing these old water hogs with a new low flow unit so the cost can be quite reasonable. I would suggest you go to the top of this forum's page and click on "Toilet Reviews", then on "Shopping" and finally on "Toto Toilets". There you can see most of the toilets in the Toto line and view their specs. Toto is the largest manufacturer of toilets in the world and has refined the low flow flushing to an art. Many of the old line brands tried to use their old designs with less water which of course didn't work. This gave low flow a bad reputation which still prevails among the uninformed. Toto on the other hand reconfigured the inner working of the toilet so it performs like a toilet should with less water. Some models now are down to 1.28 gallons per flush and a new model is coming out very soon that uses even less! The 1.6 versions are still very popular. Toto toilets are as close to being non-clogging. Most of use owners don't even own a plunger. Toto toilets are not sold in Big Box stores, but they are available from plumbing shops either from stock or order. Online purchasing is another possibility, but if you go that route, open the carton(s) and inspect them very carefully before accepting delivery. Breakage is fairly high when shipping individual toilets. Even if you are successful in getting the old toilet functioning, I would opt for retiring it ASAP.