If the tail lights are always working and only the stop light is temperamental, then it means that the cable connecting the tail lights and the stop light may be broken, or there is a loose connection in the stop light itself.
For north american accent's, it's all on the left side. The connection between the tail and stop lights occurs at SM28 (near the strut tower), then goes through connection MR3 (roughly behind the gas fill cap area) which then goes to the hood via the left hinge. Not sure if the wirings on the same side down there, but if its mirrored, I'd guess it would be roughly the same, just on the right.
I was having a similar problem with my 97 Accent, the center break light wasn't working at all. I checked the fuse and bulb and tested the connection with a mulit meter and everything seemed fine. Finally i tried taking a small steel brush and cleaning the connection for the ground (black) wire and its been working fine ever since.