I realize it is easy to recommend spending other people's money, but really it is folly wasting time and money repair a 1983 toilet that wasn't a very good one even when new. Few of us will keep trying to patch up a 28 year old Yugo, but that's about what you are trying to do. Even if you can find the needed parts and stop the leaks, you still have a 5 gallon per flush antique. The toilet brand most favored on this forum is the Toto. There are many models to choose from, some very expensive, but many that should be within reach of most anyone. Avoid the builder grades found in major discount stores. Yes, the price is tempting, but they are fraught with problems from the very beginning. Toto toilets are not sold in discount centers, but are available from plumbers even if they do not stock them. The Drake models are quite popular and would be a good choice.