Toilets, Sinks, Showers, Tubs and Disposals - Leaky Toilet - Only when tank is full

I have been struggling with fixing this problem for a few weekends now locating the leak that appeared in my basement ceiling - At first I though it was the wax ring so I replaced that - then I took the tank off and replaced the bolts and ring making sure all were seated properly. The leaking starts after the water has been in the tank for over 3 hours but I can't pin-point the exact place of the leak other than I see the water on the floor behind the toilet. When I shut off the water and flush it, the leak stops. My suspicion is that there is a hairline crack toward the top of the tank and I need to replace the toilet since this whole thing started out of the blue. Any suggestions would be helpful. Thanks, M

Put some red food coloring in the tank - and see if that helps identify the spot that is leaking. Scotch taping bits of toilet paper to various spots around the bowl/tank is another method of narrowing your search.

If I had to guess - I would think it is leaking at the gasket between the tank and bowl. Use caution when tightening those bolts - it's easy to crack the base of the tank by overtightening.