Because the horn on the outlet of the toilet is usually a fair amount smaller than the ID of the toilet flange, unless there's a clog, it just acts like a funnel, and you may never notice a water leak until the line clogs again. BUT, because the trap of a toilet is internal to the toilet, it CAN leak sewer gasses. So, yes, you should buy a new wax ring. Now, to complicate things a little, there are a few reusable toilet seals - from a closed-cell foam ring to funnels with O-rings that could be used and reused. Wax is a lot cheaper, and works well, but only once!