I wonder if something is still stuck in the trap of the toilet, or that it’s gotten so abrasive that it’s catching on stuff. Are you only flushing TP and things that exited your body? Nothing else should be flushed. No flushable wipes. No condoms. No feminine sanitary products.
But I just replaced 2 toilets on a rental because I was sick of dealing with the garbage design of 20+ year old eljer units that were constantly leaking from the tank (every year or 2 I was replacing the insides, bad design for the tank to bowl flange and bolts) A new toilet runs anywhere from $90-250 and should only take a couple of hours for install. I’m perfectly happy with, and prefer, the cheaper toilets. And for 90$ and a couple of hours, I don’t have to worry about water damage on my ceilings anymore.
As fishindude said upthread though, it’s typically not the toilet. Make sure the plumbing is clear, proper sized, and slopes correctly.
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