Noleman:
I haven't used the referenced tool listed above, but I HAVE used the chart listed elsewhere. Look up Marlin Owners Forum. Scroll down to the REFERENCE section. There's a thread there on date of manufactuer. (It's by a guy who calls himself Willys something or other) Your 30AS will be listed under the "after '48" section. Just check the letter/serial# against the chart. It's very easy.
Speaking of dumb-if I were sharper, I'd know how to simply list an address you could click on to get there. Sorry.
I have a 30AS among my Marlins, too. Wonderful little rifle. Took two deer in November with as many shots on the same day. Great shooter.
Good luck!