As a guy who had close to a gallon of cooking oil spill onto his cabin floor, I can tell you that most of the smell and greasiness went away once I took dish washer, sprayed it all over the carpet, spilled some water in there, took a brush to it, then took a nice big sponge, started soaking everything up little by little. Had to repeat.. I guess you could try cleaning where the oil actually spilled which you probably have, or at least try using some dish washer soap to cover up that area. Id also start leaving a crapload of air fresheners everywhere and keep spraying febreeze all over the interior. Leave the windows open alot. Overtime it may get better. Just some ideas..
You basically want the bad smell molecules to get replaced or out numbered by the good ones