By looking at its stock price, trading right around all-time highs, you would never suspect that Costco Wholesale may not be quite what it once was.

To suggest otherwise is heresy on Wall Street, especially if you throw in the company’s fortress-like balance sheet and cash flow statements. And let’s not forget that dividend.

But for retailers, you also have to look same-store sales — usually defined as sales of stores open more than a year. And at Costco , if you go back more than a year — and strip out the impact of gas inflation and foreign currencies — sales have been on a slow bleed for more than a year, slipping to 5 percent last month.

Add back gas and foreign currency, and they’re in freefall — a disappointing 3 percent last month, a quarter of where it was a year earlier. And while renewal rates remain robust, in the past quarter there was a pronounced deceleration in shopper frequency.

All of which raises the question: Is Costco broken?

Remember, we’re talking about one of the best companies in America and certainly one of the greatest retailers in the world. With only a few exceptions, its revenue growth going back to the early 1990 has been in the double-digits. Part of that is the result of a steady stream of new store openings in the U.S. and abroad, rising membership fees and uncanny customer loyalty.

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