Picked up a new XS7 in 7mm-08 less than two weeks ago -- haven't even cleaned, loaded, or fired it. As I was checking to make sure the screws in the scope mount base were tight, I noticed one was loose. The screw was broken. So now I have a brand new gun with a broken screw threaded into the receiver. What are the chances of getting that out w/o screwing-up the threads?

Call Marlin and have them make it right.

800-544-8892

If the female threads in the receiver are still good it would be silly to send it back. Any decent gunsmith should have an easy out set to remove the screw. Pull all the screws out and clean them and the holes with acetone. Then put the base back on with red locktite (the kind you need to heat to undo). Torque the screws @ 25 ft inches, let it set up 24 hours and your problem is solved. Did my buddy's XS 7mm08 and my XLC 270 this way and both have digersted 100s of rounds with no issue.
My XLC 22-06/270WCF

Oldman is right that any decent 'smith should be able to fix you up but this is a brand new rifle right out of the box and I'd want Marlin to know about the problem.
If they agree to fix it AND pay for the shipping, I'd send it to Marlin.

The local smith at MidSouth in Wagram, NC took care of it -- $5 and 5 minutes. Shipping to Connecticut would have been much more than that. . .

Thanks for the input.