DETROIT — It’s virtually impossible to buy a car these days that comes with a set of shot glasses.The 1957 Cadillac Eldorado Brougham, though, included not just a set of shot glasses but also Arpege perfume, Fleetwood cigarettes and a powder compact in the purchase price of $13,074 — about three times the cost of a regular Cadillac and pricier than a new home in an upscale area at the time. Only 400 were built.Today the vanity kit alone is worth as much as the car.This is but one specimen of perfection at a nondescript location in Sterling Heights.A temperature-controlled showroom displays 165 vintage cars at a time of 700 owned. Each visit to the rotating exhibit offers a glimpse of something different. Designs range from 1902 to the present, concept cars and road-tested. Many vehicles have been purchased, reclaimed and restored after collectors died. A purple 1967 Pontiac GTO hidden under the sand of the Arizona desert was dug up, cleaned and refurbished.For car collectors, the site is a jewelry box filled with precious gems. These include the most celebrated cars of our time, and those featured in Beach Boys songs and driven by Elvis Presley onscreen.The unpublicized collection is somehow attracting visitors recently from Sweden, Australia, Poland, Kuwait, Egypt and Sudan.Viewing is by appointment only. Callers schedule visits months and years in advance.While access at the locked front door doesn’t require a secret handshake, it probably should."Holy smokes. I’ve never seen anything like this," said Robert Wall, 89, a Detroit native who has attended every Motor City auto show since 1937. "I had no idea this existed. I couldn’t have imagined this in my wildest dreams. I could stay forever."He was rationed to 90 minutes.To those who know nothing about cars or think they care little, there are simply no words. This is a design mecca.Everything is labeled with historical explanation and auto industry impact.All this chatter about electric vehicles and innovation? Check out the enormous battery under the hood of the 1966 Electrovair II Experimental car.GM may be considered a front-runner on electrification today, but it’s clear the institutional knowledge spans decades, said Greg Wallace, who has helped develop the collection over the past two decades as manager."The collection tells a story of the history of the automobile and our fascination with car culture," said Jonathan Klinger, a spokesman for Hagerty, the world’s leading classic-car insurer. "You’re actually able to study the thinking and innovation of the company and see how things were applied or not applied to production vehicles."Visitors learn that the word "cranky" comes from drivers in the early 1900s having a bad day crank-starting their cars. The crankshaft would kick back and break a thumb or a wrist and, on occasion, come out of the crank hold and hit the operator in the head, Wallace said.Vehicles from the 1900s have headlight covers that open to reveal a lantern wick inside. Steering wheels in 1912 were on the right, not left.Matt Anderson, curator of transportation at the Henry Ford museum in Dearborn, said classic-car junkies can’t help but savor trips to the Heritage collection."All of the significant show cars are there — the Y-Job, the Le Sabre, the Firebirds — as well as the company’s iconic production cars — the Tri-Five Chevys, the 1959 Cadillac, the split-window 1963 Corvette, the 1977 Pontiac Trans Am Special Edition," he said. "But there’s also a strong collection of technologically significant cars — not as flashy but equally important."I admire GM for saving examples of less-than-stellar products, too," Anderson said. "One of my favorite vehicles at the GM Heritage Center is a 1976 Chevrolet Chevette — no one’s idea of a collector car today, but one that sold in the millions in its time. Cars like the Corvette made GM’s image, but cars like the Chevette made its bottom line."In the beginning, the goal was just to try and preserve history, Wallace said."I had no idea it would turn into what it has," he said. "Once history is gone, it’s gone. I wanted to make sure we could tell our story down the road."