Hi, few months ago, I had a bottom leak, bad wax, and I had a plumber replaced for me. Months later and now I have another problem with this toilet

I have been hearing water filling every few minutes as if water is leaking.
First I change the fill value, and I thought i fixed the problem, but the water is still refilling itself (with noise) Then I opened the toilet lid and realized that there are some bubbles inside. Do you think i need to change the flush valve? (that is the only thing that I didn't realize yet)

Speaking of flush value, years before I remember I changed the flush valve on other toilet and the toilet to tank gasket does not fit. I thought it was standard, I bought some from home depot, and they don't fit, so I ended up using the old one for that toilet. I am afraid this time if this toilet to tank gasket is bad, then I don't know what to do. What brand of toilet to tank gasket fits all??

FYI, the toilet i have is 2 pieces toilet where you have the tank and the toilet part itself.

Please shed some lights on my problems, Leaking in flush value ?

let the tank fill all the way.
put some food coloring into the tank.
if the food coloring shows up in the bowl, change the flapper.

flapper replacement can be a pain.
sometimes a universal one will fit and work.
other times you have to get the exact manufactures replacement

perhaps the refill tube is inserted too far into the overflow tube

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638