Paul,
It sounds like you've isolated the issue to the coax cable pass through located just behind the antenna hand crank cover plate. You may have to carefully poke around to locate the pass through.
Here are a few links that may be of help;
https://www.trailmanorowners.com/for...ght=tv+antenna see post #3
https://www.trailmanorowners.com/for...php?albumid=49 some helpful photos
Let us know how you make out.
Dick