[C320-list] Thru-hull sealant failure

[Jeff Hare]

At the risk of over-posting, I noticed something unusual while spring
cleaning on the boat.  Just in front of our regular engine raw water intake
is a second (identical) thru-hull fitting which is capped.  I presumed that
it would be for AC or something, but it's never been used.  I'm the first
owner and it came this way but could possibly have been a dealer installed
fitting?  Anyone else have one of these?

Anyway, the white sealant around the base of this fitting seems like it did
not cure or somehow got softened recently by something.  I can mold it by
pressing firmly on it.  Then you end up with some sealant goop on your
fingers.  :(   I'm pretty sure that this was not like this years ago so I'm
wondering whether any kind cleaner might have softened this material.  I'm
also certain I wouldn't have gotten any 3m adhesive solvent anywhere near
this, but perhaps something else like penetrating oil or something got on
it?

I noticed it last spring and now that the boat's out of the water I'm
thinking I should dig/scrape it off and clean the outer uncured bead that's
soft and if it's just a surface sealant failure, put a fresh bead of 5200?
around it.  There's just no way I'm pulling this thru-hull out this year and
it's pretty unlikely that it'll ever be a problem since there are no leaks
or signs of failure when looking at the outside.  The main raw water intake,
nor any of the other thru-hulls show any of this tendency.  They're all
solid.

Does anyone have ideas here?
-Jeff Hare
#809