wax ring on bottom leaking to the floor needs to be replaced
if it is a leak inside the tank flapper needs to be replace this problem occurs a lot if you use Bleach in your tank the rubber flapper gets soft
The ONLY places any toilet can leak is between tank and bowl, or between bowl and floor.
If leaking at floor when flushed, wax ring needs replaced. If water leaks between tank and bowl when flushed, tank to bowl gasket needs replaced.
A new head gasket.
the shift in weight from the new tank may have caused a shift in the wax ring and gasket where your toilet hits the drain pipe. wax rings only cost about $3-$5 and are easy to replace with a friend.
Gasket that goes between head and valve cover to prevent leaks
A failed head gasket will have different symptoms depending on where the gasket failed. If the gasket fails in such a way that coolant leaks it usually leaks into the oil reservoir and the oil will appear a milky light tan color. The coolant also may leak out of the gasket onto the engine, appearing between the head and the block. If the gasket leaks in such a way as to cause loss of compression the engine will idle rough or will not want to idle at all. If the gasket leaks oil it may end up in the cylinder(s) or come out between the head and the block. Also, any combination of the above described leaks may happen in conjuction with one another.
Oil/antifreeze mix is usually caused by head gasket leaks or valve cover gasket leaks.
When it leaks.
A common cause of problems in cylinder head gaskets is leaks in the gasket. When a leak forms, the gasket must be replaced.
Most often that indicates the presence of water or coolant in the combustion chambers. Common causes are head gasket leaks, intake gasket leaks, warped head/s or warped intake.
it leaks oil
You have a failed gasket, seal, or hose.