"I realize it may be the only way"

Good guess.

What an amazing coincidence. We just found water damage in a lower floor bedroom, below the second floor master bath. First, our contractor cut some holes in the ceiling and, when the tap in the master bath was turned on, we could see water coming down between the floors. The contractor then removed part of the siding on the second floor, behind the master bath sink to expose the pipes. There was a hole the size of a quarter in a 90 deg. turn of the drain pipe. There was no rust or corrosion--just a hole. Our contractor speculates that a plumber's snake to clear the drain punched the hole. Over the years, this drain has been cleared a number of times using a plumber's snake. The plumbing joint was replaced today---but sheetrock is still being removed in the lower bedroom to expose the water damage from the leak. I don't know how your plumbing is situated upstairs, but it may require some demolition in order to locate it. Perhaps a different plumber would be willing to try a pipe snake camera.

You may also be able to have a home inspector scope the drains.

Repairing a ceiling is not that hard.

Cut a hole large enough to get a mirror through and look around.

Our shower stall leaked and caused a wet spot to appear on the ceiling below, but only infrequently. We had the shower pan replaced, thinking that was it. Finally we discovered it was the shower stall itself.

Thank you all for your comments. I almost feel like buying a plumber's snake camera to look around myself but they are expensive. Every time I call a plumber, I take a chance about whether or not they will use it. (I make sure they at least have one before I give them the address). I am already out $200 and still no progress. Unfortunately, I have not been able to find a place that rents them out. At least if I could find the leak, I could point them to the right place. Does anyone have any experience with brand names of snake cameras are good and what to look for?

I have seen a lot of posts about people having to get their pipes snaked only to have leaks start a few days later. My company started selling a product called BioClean. My bathroom sink was getting clogged up and my boss let me take home a tub of it so I wouldnt have to pay for a plumber (family issues made money extremely tight at the time). After a few days my bathroom sink started flowing like normal.

I realize advertising is prohibited, But you might want to look into something like BioClean as a monthly maintence program, instead of getting your pipes snaked every few months the organic bateria in the BioClean will help control the amount of material clogging your pipes. There wont be any damage to your current piping system and you wont have to worry about harming the enviroment since it is organic bateria.

Here is a link that might be useful: Information on BioClean

"At least if I could find the leak, I could point them to the right place. Does anyone have any experience with brand names of snake cameras are good and what to look for?"

Unless you have a very large hole or a pipe completely disconnected a drainline camera is not going to show you very much.

The insides of pipes are not very clean or smooth (especially if they have been in service) and a small leak or cracked is not going to be visible.

You should count yourself lucky none of the plumbers have wanted to take your money for a waste of time.

Even with a camera, it can be hard to figure out where the camera is in the pipes after a few turns.

Main lines tend to be pretty straight form the street to the house, but under-slab drain lines can have enough bends to make tracking the camera very hard.

With plastic lines you can use a camera detector to locate the camera in the pipe (they give off enough electrical noise from scanning their image device) bit in cast iron lines (and then under concrete) the signals are very weak.

The detectors are sold to allow a stuck camera to be found and removed.

My thought was to put a hole or two into the wall/ceiling, not the pipes, to look around for moist/wet areas on adjacent pipes, flooring to identify the spot/area that is involved. Is that a possibility?

Just cut a small hole with a rotozip and use a mirror.

Save the piece of drywall and use it to repair the hole.

You are making it way more complicated than it needs to be (and I own flexible and rigid bore-scopes).

The big question is, are they cast iron drainpipes? The plumbers doing the snaking may not have done anything wrong, those things can be rotten.

Don't delay, get a drywall handsaw or rotozip and carefully cut an inspection hole. Ceiling under is probably the best place to start. Drywall holes can be easily fixed.

Thanks Everyone. I am not blaming anyone for the leak...and yes, they are cast iron pipes unfortunately. Any other suggestions welcome.

No worries. I doubt you are going to get a magic, better answer. You mustn't delay further, you're risking mould and a permanent smell....

The drywall is easy to fix.

If water is coming through the ceiling, then the ceiling needs to be repaired anyway. So cut out the damaged area and get a good look. Repairing a 4' by 4' area is not much more difficult than repairing a 1' by 1' area so cut out an area big enough to get a good look and also make the repair. I suspect a rusty drain broken open by the snake - if so replace with matching size PVC and couple together with rubber pipe coupling - see pic at link below.

Here is a link that might be useful: Pipe Coupling

And here is a site that can help you with the drywall repair. See link below that gives a detailed10-step video series on such a repair:

Here is a link that might be useful: Drywall Repair

Repairing an area that has framing on two edges is easiest.

Cut the drywall to the edge of the framing, apply some 2x2 'sisters to the bottom edge of the framing in the opening, attach patch to sisters with drywall screws.

With a Rotozip you can cut the opening cleanly and use the piece cut out as the patch if it is not otherwise damaged.