This old timer at the Oshkosh airshow showed me a trick for finding a bad coax connector
I was helping him set up a portable ADS-B receiver in his tent, and we kept getting signal dropouts. He pulled out a little spray bottle of isopropyl alcohol and misted the BNC connectors on the antenna cable. He said, 'Watch for the one that steams up fastest, that's your leak path.' Sure enough, one connector fogged up in about 2 seconds, showing a tiny crack in the seal we couldn't even see. Has anyone else used that trick on old fleet birds?