Oh, but it is dirty! (1)
Our first impression of the place is one of filth. And exclamatory filth, to boot. Sure, the speaker is merely describing the station here, but there's also a judgy tone to her evaluation. We can just see her rubbing her hands with her handkerchief, saying ick!
oil-soaked, oil-permeated (3)
Not surprisingly for a filling station, it's greasy. But for it to actually look greasy, it's got to be pretty extreme. It's as if everything in this joint has become one with the purpose of the filling station. Everything is oily.
to a disturbing, over-allblack translucency. (4-5)
She said it, not Shmoop: this place is disturbing. Again, she's getting judgy. What's so disturbing about a gas station being oily? We mean, isn't it supposed to be?