Is there visible corrosion on the F connector or around the cover plate on the LNB? It may have been dropped and not water damaged if there's no visible corrosion. If you hear a rattle inside there's a ferrite bead on a plastic screw that may have broken. I have a three Norsats here broken like that, 2 used and one brand new, they get about 16 for signal.
The new one was damaged in shipping and the company replaced it no problem, the used ones I'd broken being clumsy and falling off my step ladder. If it is water damage to the F connector, replacing it as Waylew explains how to should be fairly easy to do.