I am considering the purchase of an American 180 (Select Fire) from a local friend. Comes with 3 barrels, 6 magazines, and has been well taken care of. Is there anything 'specific' that I should be looking for, or at? Any recurring issues with this type of weapon? Just wondering if there are any 'indicators' that I should be aware of. It has already had some of the 'upgrades' done to it. Thanx for any ideas or suggestions!