KGC wrote:
My concern is that there may be leaks further up this pipe. Is there any way to detect such leaks without tearing out the drywall on the main floor to view the pipe?
To answer your question - Looking for leaks below bathrooms is something I do during every inspection with my infrared camera. I think infrared is really the only way to find hidden leaks unless you had a good moisture meter and covered every square inch of ceiling with it.
BTW, if the leak is at the elbow but you are wondering if the actual leak is further up the pipe, it should be easy to see traces / water stains on the bottom of the pipe going towards the elbow.