Greetings all!

About 6 years ago, my wife and I bought the shell of a an unusual
house. Construction started around 1979, and then after a few years
of on-again-off-again building, the house was allowed to dilapidate
for about 15 years. After purchasing the house, we completed the
construction job with the help of a resourceful contractor. All the
interior plumbing, drywall, electrics, etc. was done around 1997.

Here is the problem: The pipe from the first floor bathroom sink
basin leaks. We know this because, fortunately, the basement ceiling
is not yet finished, and we can look right up at where the black ABS
pipe comes down from the first floor and we see the water dripping
down the pipe. Behind the bathroom sink, the pipe goes horizontally
into the wall, then must turn down 90 degrees and then presumably does
not turn again until we can see it above us when standing in the
basement. When in the basement, we see the water leaking down the
pipe, but since the pipe disappears into the framing above, we can't
see the source. Therefore, I am guessing the only reasonable source
of the leak is in the wall where the pipe makes its 90 degree turn
downward. Does this sound reasonable so far?

What approach do I take to repair this pipe? Fortunately, there is a
bedroom dresser on the opposite side of where the sink pipe goes into
the wall, so I guess I can cut into the drywall and locate the faulty
join. How do I fix it when I find it? Some kind of miracle epoxy, or
do I have to cut and replace the pipes?

Also, although it is probably too much to hope for, is there any
miracle product I can run through the pipes to seal the leak without
me having to cut into the wall?

Also, one wonders why ABS pipe would leak so soon after installation.
Perhaps faulty workmanship is to blame, but then I found out about
this class action suit pertaining to defective ABS pipes:

http://www.abspipes.com/id.html

I don't know yet if my pipes qualify, but I intend to find out. Does
anyone have any further information or experience with this class
action suit?

Thanks in advance!

Chuck