As installed by Verizon, the cat5e/cat6 cable does not plug directly into the Ethernet port of the unit.
Instead, there are terminals for each wire pair (see photo).
If one were to open the snap-close terminals, one would find that a clear substance (slightly sticky, a little viscous, been applied to each terminal, perhaps as an oxidation inhibitor or to keep dust out.
What would the clear substance likely be? I seem to recall the Verizon technician applying it when he installed it several years ago.