thanks! i'll try. things are a little better now because i finally got the snake through to the basement. so, the pipe still drips, but it doesn't pour water straight out.
it's hard to get a good angle to see anything in there. one thing that's cool is that by turning the flashlight on my phone and sticking the camera in, wigling it around, i can kinda get a view of things. i guess a mirror would do too, but i kind of wish i had a fiber scope of some sort.
my current theory is that a kitchen remodel before i bought the house moved the sink to the right. previously, this pipe went straight down. then they cut the pipe, ran a plastic pipe though a wall strut to the right to drain the sink in its new location. ( then they built cabinets with no pipe access over the whole shebang. )
it's probably the elbow between the two pipes that's leaking. ( and it might have been happening for a long time, it's only when the pipe got blocked up that it became noticable. )