Wilson's garage is very isolated. However, Wilson is not selfish at all. He is struggling just to get by, while Tom teases him with the possibility (which we know he'll never follow through on) of giving him one of his many cars.
This isolation is the product of the East Egg way of life. They buy/take what they want, and when they are through with it, they dump it. It is no longer useful, so they simply leave it behind. Wilson's garage is like that. Tom uses Myrtle for his own selfish needs, then dumps her/leaves her dead body behind when she's hit by the car. Because of the way that George and Myrtle are treated, they have been isolated by society. They are only needed for one thing, and then they are left behind. George works on cars and offers gas, while Myrtle entertains Tom for a short while. Both are left behind since the Valley of Ashes sits out in the middle of nowhere, and people only pass by taking what they need and leaving.
Beyond West and East Egg lies Wilson's garage. It is a place described in Chapter Two as "small block of yellow brick sitting on the edge of the waste land." Since it is the only building in this "waste land" that is known as the Valley of the Ashes, it symbolizes the poverty and isolation which existed beyond the glamorous neighborhoods of New York. Here, people like Wilson and Myrtle lived a very different life to people like Tom and Daisy Buchanan. This idea of isolation is further supported by Nick's description of the interior of the garage: a place which is "unprosperous and bare."
In terms of selfishness, the garage, perhaps, represents the selfish ambitions of Tom and Myrtle. Tom believes that it is good for Myrtle to get away from such a place, even though he is cheating on his wife, while Myrtle is happy to enjoy an extra-marital romance in the city while her husband thinks that she is visiting her sister.