I have the same problem with my replacement slider. I am not sure if it is not a brand problem. Same supplier where I got my slider did not have supplier for the replacement for power cord hole cover. You might take yours to different outfitters ...
I level with the slide side high, drop the stabilizers, extend the slide and hope the door to the head stays closed. If the trailer is not level to slide side high the door to the head swings open. We don't latch it because the cat's litter box is ...