I have a roughly 12 yr old Gerber 28-790 toilet that will run for 2-3 seconds every couple of hours or so. I have replaced the fill valve (fluidmaster), the flapper and the seal on the bottom of the flush valve. I have not replaced the flush valve or the seal between the bowl and the tank. Mainly because I am having issues find the correct parts in a store. I have tried adjusting the water level several times to no avail. Not sure how high or low the water should sit in the bowl, or if it matters. Tried the food coloring test, nothing running down the sides of the toilet but the water was blue in the very bottom of the bowl. It looks like a leak from the tank to the bowl? Maybe the gasket is bad? I do notice some small air bubbles around one of the bolts that holds the tank to the bowl and around the flush valve seal. Maybe they need to be tighter? I have them really tight now not sure what the deal is with that. Any help would be appreciated! Thanks!!