My marker/clearance lights are not LED. When I was changing a bulb a while back, the lens broke in my hand, weakened by age and exposure. Same thing happened a few months later. I now keep a couple of each color on hand. They're cheap and readily available.
As to sealant, I mount the lens dry, and then spread a thin coating of silicone around the perimeter by finger so it seals over everything from paint to lens.
John, Diane, and Lincoln, the guard cat. RVM103
Fulltimers since June 2012
2002 Dutch Star 40, Freightliner, Cat 3126, 2004 Element