[LazyPup]

I just had a silly thought that might be helpful. You know the exact spot on the basement floor where the drip is occuring. We also know that the drip is occuring in the vicinity of the chase where the pipes go through to the adjacent floors. Use a plumb bob or any small weight attached to a string to mark the exact location of the leak at the ceiling then rry attaching a sheet of paper on that line at each level. If you note a wet spot on a piece of paper you know the source is above that level, whereas if it is dry at any level, you can assume for the moment that the leak is below that level. If you can do that at each point of access you may be able to narrow down your search quickly.