We had a really, really slow leak in our home propane range that took me a couple of years to find. There was an occasional bad smell that I never even realized was propane for a long time. Initial work with a gas sniffer yielded nothing. It was only a fluke that somebody opened the refrigerator door (a few feet away) while I had the sniffer running and got a very faint hit on it. I think what happened is that the gas built up under the range, then the draft from opened refrigerator pushed it out from underneath. It was leaking where a straight pipe was threaded into an elbow. With the range opened up and soap solution applied, the bubble blew up at a rate akin to watching paint dry or grass grow.
