air leak
If I coated the fitting in thread lock glue would that help at all?
I have two A3's and had the same problem on both. I replaced the push in air tube fittings and it fixed the problem. There are two fittings on the air switch. All of mine were John Guest plastic fittings. They are available from McMaster-Carr. Each valve has one straight and one 90 degree swivel. Below is part of my order. You will need one each.
51055K47 Moisture-Resistant Acetal Push-to-Connect, Swivel 90 Degree Elbow for 1/4" Tube OD X 1/8" NPTF Male 3.76 each
51055K971 Moisture-Resistant Acetal Push-to-Connect, Adapter for 1/4" Tube OD X 1/8" NPTF Male Pipe, Gray 1.47 each
Three of the four fittings that I replaced broke when I removed them. I had to use a screw extractor to remove the broken end. Put pipe thread compound on the threads before you install them. The easiest way to install them is to remove the switch by removing the two screws on the faceplate.
I guess that these fittings get old and start to leak after 10 or 15 years.
Good luck,
Dale