A little more info:

1) Are you using the stock flush chokes, or aftermaket chokes?
2) If the latter, is it an extended choke?
3) What loads are you shooting?
4) At what distance is it 6-8 inches to the left?
5) Are you shooting off a rest or free-hand?

Off the bat, I'd suggest shooting off a rest, looking straight down the rib like you were sighting in a rifle, and make sure your sight picture and trigger squeeze is consistent from shot to shot. If it's still shooting to the side then...
I'd then try different ammo.
I'd try different choke tubes.

If nothing helps, I'd send it to Winchester.

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