Re: Asphalt on top of old concrete
Asphalt can be put on top of concrete, it's done on highways all the time. While they do have rollers small enough to go into the garage it would not be able to get to the edges near the walls and the cracks in the concrete will telegraph through the asphalt in short order.
I would not use leveler with the amount of drop you describe in the concrete. There is an underlying problem and it would be best to tear up the concrete, do a proper base and install new concrete.
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