Weird odor in bathroom
I've read what people have gone through, trying to solve this problem, that we've had for a long time. I've pulled up the toilet and put in a new seal. The old one was fine. I've checked for leaks in the water trap and drain in the sink and found no problem. We clean the toilet with brush and toilet bowl cleaner regularly, and have an automatic cleaner in the tank. It still smells.
Recently I was sniffing out the problem and noticed it was coming from the inside the clean bowl of the toilet. I looked closely at the underside of the bowl's rim (not easy see). I spotted a dark mold crud around the holes that flush water and clean the bowl, beneath the rim. They are tucked into a corner and easy to miss even with a good brushing. With copious amounts of bleach and paper towels I killed the mold and scrubbed carefully into the underside of the rim, and like magic, the long time plague of an odor is gone!
I plan to use a stronger automatic bleach or bromide dispenser in the tank. There are simple ones that add the cleaning solution to the overflow pipe in the tank, not the tank water. Over time, bleach can be corrosive to the components inside of the tank, so this solves that problem. And we will have to be more diligent about seeking and destroying any mold buildup in the future!