Exciting Toilet question, can you advise?

[JayhawkSD]

3. You may have to replace the flapper.

And polish the seat that it seals against. If there is a tiny nick in the seat then you will have to replace the seat as well.

Sometimes a kind of slimy fungus builds up on the underside of the flapper. It will allow a tiny amount of water to pass. If it feels slimy clean it with CLR cleaner and clean the flapper seat as well. Do not use any abrasive cleaners, not even Soft Scrub. They will leave tiny nicks in the seat that will pass water.

If your best efforts don't resolve it, call a plumber or replace the toilet with a low volume flush model. Adjusting the water level did not save much water; like a proverbial drop in a bucket. 45 years is a full life for a toilet; it doesn't owe you anything and you are wasting a lot of water every time you flush it, even after adjusting the level.