The rear sun roof drain plugs are connected to a plastic hose that leads down the C pillar and drains behind the rear wheels. To see the draining end of the hose you'll need to get under the rear end. One should be next to the muffler the other by the gas tank.
It's possible a previous owner may have done a shitty patch job fixing some rust (that area is notorious for rusting out) and may have un-wittingly sealed the hoses inside the car. That's how my current Blupra was when I bought it. It too would leak on one corner and after tracing the hose I realized the draining end was sealed in foam!
at: :bad-word: :2gunfire: :jerkit: :throwup: :evil: :crazyeye: :crying: :roll:
Anyway, I believe the forward drain hose travels down the A pillar and drains into the rocker panels (someone correct me if I'm wrong). Good luck getting at that those.