Interesting question.
I had a leaking gun. Coming from the Aerospace industry, I'm normally one of those guys that use the same or similar tools at home as I did (retired) at work.
So, I bought some - "Sherlock, Gas and Air Leak Detector" to help me find the leak. What did I end up doing ? I mixed a little dishwasher soap (Dawn) and water, shook it well, (had to wait until the bubbles went away !) and then lightly sprayed at each possible leak point. Starting at the front, and moving to the back.
Easy wipe to clean and dry. And yes, it showed me exactly where the leak was.
Mike