1998 Honda Civic EX oil pan gasket leak?

I have a 98 Honda Civic EX (=aluminum oil pan).  A month ago the dealership did an oil change and told me (1) I'll need a new oil pan or a time sert soon [=first I'd heard of any difficulties with the drain plug], and (2) the gasket on the oil pan is leaking.

I had just had the gasket replaced around 14 mos ago.  I took it back to the shop that replaced it and they said it wasn't leaking, took me out to the car on the lift and gave me a flashlight.  It didn't look like there was a leak, but the oil pan looked quite clean on the outside (=no road dust etc).

Now, one month later, I have lost around 2 or 2.5 quarts of oil.

Is it the oil pan gasket?  If not, where is the oil going?

Thanks.