My house is quite old as is the toilet in question. I have not had any problems prior to last week. The flush lever broke and I had to replace it. The internal parts of the tank have been replaced with Fluidmaster parts but this has been a few years ago. I have not observed any external leaks and have not heard any signs of leaks such as gurgling or water draining.
I noticed the other day that after flushing, the tank slowly loses water until it is about 1/2 the level it used to be. I have read that this could be due to the vent and/or air pressure. I have a second bathroom with a toilet and that toilet is operating fine.
My question is why would this just start happening now? If it is a vent or pressure issue would it affect both toilets?
I am not a plumber. I am handy around the house but not an expert. I am out of work so can not afford to call a professional at his time. This seems like it may be something I can handle on my own. I would appreciate any advice or input.