"Caulk" for Rock Guard

[Toasty's Dad]

Spousal unit wished to renovate the spline around the flat center plexi rock guard for the front window of our 2004 Bambi.

In order to do this, we of course had to remove the guard from the trailer. Under the hinge was some remarkably pliable white putty or caulk, still flexy and sticky after all these 13 years.

She wants to use the same or similar miraculous substance when we replace the guard. Does anybody know what this stuff is?

Thanks!
Jon