Well, if it is plastic I would skip the heat and just use a liquid solvent cement. I apply it with fine needle nose forceps using it like a drafting pen. You can lay down a fine line along the crack. Let it sit for about 20 seconds to soften the underlying plastic. Then lay down another line and lift gently up holding it there for a few minutes. Tenax 7R or its replacement Micro Mark Same Stuff evaporates pretty quickly and may not damage the paint if you are careful.
Shame on Lionel for using plastic for this vulnerable part.
Pete
