American Express ($AXP) is Warren Buffett's 5th largest holding and his largest of Visa, Mastercard and AMEX by far. Market weakness has driven this dividend aristocrat down 12% in the last year. Is this a stock to buy now? Or does this payments giant have some skeletons in the closet? Disclaimer: This is not personalised financial advice and should not be taken as such. If you require personalised advice please consult a professional financial advisor.