Had an interesting leak just a few weeks ago. Every once in a while, while checking before a trip, I'd find my inner rear dual leaked down to zero. Use my little pump to get it up to 25PSI and limp to a truck stop to top it off at 90PSI. Then off I'd drive, checking periodically. On the road, it would always be right. And it would stay right. Sometimes for weeks.
Three times over a years time, I had it removed and checked by a shop. Immersed in water and all. Never found a leak. It was a head scratcher and the shops had no idea what the problem might be.
Finally, it did it at an RV park right across the street from a truck tire shop. Got it up to 25PSI, limped across the street, explained the problem and they had the tire off before the day grew warm. Immersing it in a tank, it showed bubbles coming from the wheel!
With the tire off the rim, we could see tiny rust through spots in the rim. Just two of them. What was happening was that overnight, on cold nights, the rim would shrink just enough to allow air to escape. Driving it a while would cause the rim to expand enough to choke off the leak. So once the tire was warm it wouldn't leak. This explains why 3 shops couldn't find a leak. Why I could drive for weeks at a time without it going flat is a mystery.
They checked around for a new wheel with no luck. So I had them clean up the area around the holes, and we put a couple of Eternabond patches over them. No leaking so far. Another use for Eternabond.