What is this part called

[RvReno]

Hello - There is (was) a long plastic strip that went in a channel that covers the screws the hold the gutter. It became completely dislodged and fell out on its own. Of course this happened a few months after warranty expired. It looks important to keeping water out. Does anyone know what it's called and where I can get another? I want to call it weather strip, but that does not seem complicated enough. Thank in advance!