The toilet tank valve seal is creating a black goo that is getting on the porcelain surfaces in the tank and in the toilet bowl. I've read that this black goo happens to black flapper's when they age and the only fix is replacement. My questions are, is the tank vale seal going bad and will it need replacement? If the tank valve seal is going bad are there any non-black seals available so this won't happen in the future? Also what can I use to clean/remove the black spots from inside the tank and bowl areas? I've tried bowl cleaners but they do not fully remove the spots.