After I found a hairline but large crack in an elbow I knew the others could be very hard to find. especially if not in plain view. So I used water back through the jet and suspected another crack nearby but not positive. It was on the back side and I couldn't tell if it was just spray from my known leak. Then it got dark and I thought of using a flashlight. Bam! there it was.I used a flashlight to shine inside jet opening(from inside the tub) and held a mirror on the back side of fittings(underneath). The cracks showed up like neon lights.

You've just given me a few god ideas....thank you!