You may need to regas (gas can include a dye visible under ultra violet light) in order for them to find the leak. They will gas and then check it again in a couple of weeks to try and see where the leak is. They can then repair the problem and may need to regas again.
I am never wrong.
I thought I was wrong once, but I was mistaken.
Three people can keep a secret...but only if two of them are dead.