Always try it before you mess with it.
Run about 100 rounds of a VARIETY of loads and then take it apart to inspect for anything that may be wearing oddly. (This assumes, of course, that you make it through that 100 rounds without issue. Issues related to the shell stop can make that first 100 rounds tedious if there is a problem.)
Things to check at 100 rounds:
Is your magazine tube getting scored from the secondary gas system? Letting it continue will cause damage to the magazine tube, a return for service issue.
Is your return spring showing signs of eating into the plunger? Letting it continue will cause damage to the return spring tube, a return for service issue.
Is anything working loose on the gun? (Rail screws, etc.) These issues usually show up in the first 100 rounds.
Most other issues either take a lot longer to show up or have no real 'warning signs' of failure. Many of them are addressed with non-OEM parts anyway, so no return to Mossberg is necessary.
Since your 930 is a Waterfowl model, the piston and magazine tube will be blued, rather than the Boron Nitride of the JM and DC Pro models. These will be areas to watch carefully during and after your initial break in as corrosion is common in some environments and can result from simply sitting in your gun safe after a session.
William
http://www.OR3GUN.com