I have a new Goodman GMH95 furnace, installed several months ago.

Recently I've noticed water gathering around the base of the exhaust
pipe. I've wiped it away and watched it slowly accumulate around the
base, as if it's coming from the coupling of the pipe to the furnace
itself (not from some exterior source). The screws holding the
coupling to the furnace are rusting, so evidently this has been
happening for a while but I just noticed it recently.

Any ideas as to why this might be happening? Should I just apply a
sealant around the pipe where it joins the coupling? Thanks in
advance.