Oil stains and solvent odor in garage

I bought a house in Fort Collins, CO, with a three-car garage that the seller used to work on old cars. It has lot of oil stains on the garage floor and smells like solvents.

I tried a couple of cleaners with a pressure washer, and they had little effect. Do you have suggestions?

A neighbor suggested TSP, which sounds reasonable.

Eventually I might coat the floor with an epoxy paint, but that probably has to wait for warmer weather, and I need to make progress on the stains if I expect the paint to stick.