My one toilet is over 60 years old, uses 3 gallons per flush and the only thing I’ve ever had to do is replace the rubber seals every 10 or 15 years or so when they harden up. I like it and it will handle anything that gets into the bowl from Mr. Stinky to the occasional diaper. I also have one of those water efficient ones in my other bathroom and I fail to see the economy of flushing 3 or 4 times to clear the bowl.
Anyone who is flushing more than once, needs a newer toilet, it took a while for the manufacturers to catch up with the laws.
You must be doing something to your 60 years old toilet to make it a 3 gallon flusher, because those used to be 5.5 to 7 gallon flushers.
The 3.5 toilets from the 1980s were pretty bad also.
Once the states started passing laws regulating toilets the manufacturers asked the feds to make national standards.
I don’t know when federal involvement started but in the sixties toilets had already gone to 5.5 gallons from 7 gallons and that was followed by 3.5 gallons in the 80s, then the 1.6 in 1994.