In the smoky environment of a grill, the thermocouple may well get a buildup of creosote. I suspect that is why Traeger placed the ceramic cap on the thermocouple. I accidently bumped mine when I was cleaning up following my last cook. I purchase a tube of Permatex Red High Temp Silicone Gasket Maker and used a toothpick to cover the tip of the thermocouple with a thin layer. Hopefully, the silicone will protect it from buildup and since the silicone is flexible, it should not be as easily damaged as the brittle ceramic.
The Red silicone is supposed to withstand intermittent temperatures up to 650 degrees F, so it should last. It is designed for use on automotive sensors, so it should be OK on the thermocouple.
I just coated it yesterday, so I am waiting for a full cure before testing the grill.