Actually, thanks for reminding me to check that. I have a 10 meter antenna on the truck also and have just reconnected it to test. No problems, so it is probably just that cheap Jetstream antenna.
Be advised that the test does not rule out the SO-239 at the rig yet.
Could be a situation where the center pin for your 10-meter setup may be a wee bit larger in diameter than the one for the other antenna, making a better connection at that point.
Should be easy enough to examine both plugs side by side, looking for wear or a difference in the pin diameters. Also eyeball the socket side on the radio, paying particular attention to the center fingers and also to look for the possibility of a bit of corrosion there, easily cleaned with a wee bit of Deoxit spray and then inserting the connector a few times while still wet to get some mechanical wiping action in play.
GL es 73