Are these the screws on the top of the cover part, for attaching it to the base part? If so, I don't think they need to be sealed--at least, mine never have been. Any slight bit of water that gets down the chimney part of the fridge area can exit via the lower vent, the same as any water that sneaks in via the lower vent. I would suggest using stainless steel screws for those four screws, though, so you have some hope of getting them out in one piece next time.
Dicor keeps better than many products in caulking gun tubes, incidentally; just stick a roofing nail or whatever down the spout. It's good stuff to have on hand regardless.