Unit is 3.5 yrs old. Discovered leak yesterday and cannot quite
determine the the source. The thermostat and lower element are about
12 inches above the bottom of the unit, and when my husband removed
the access panel, water spilled out there. We know it was pooled up
at the top of the water heater as well, and leaking down the outside
from the top. Husband theorized that the water leaked out of the
lower element port, filled up the space between the insulation and the
tank, all the way up to the top of the unit and began pooling there.

After replacing the lower element and refilling the first time
yesterday mid-afternoon, it did not begin to leak until late last
night -- coincidentally after the water was fully reheated.

This morning, after turning the unit off, draining it, carving away
the insulation and checking for water around the anode port is, we can
tell the leak is not coming from anywhere on the top of the WH. It
did not begin to leak today until about 5 hrs later -- coincidentally
after fully reheating. It is currently leaking from the very very
bottom: there is a exterior metal skin like a pan, identical to the
"skin" my husband pried off of the top to get to the insulation and
anode. It is leaking from the seam between the "side skin" and the
"bottom pan."

It does not APPEAR to be leaking from the T&P valve.

Does it sound like the tank leaking (and thus subject to the warranty.
We didn't want to pay $100 for a tech visit -- 4 days from now, btw --
to find out it's the $15 anode)?

WHY DOESN'T IT LEAK UNTIL IT REHEATED? (this could just be our
interpretation. I had theorized that residual water is draining out
from the insulation, but it stops dripping while the unit is drained
and for several hrs after refilling).

Thanks for your advice.