Oil extractions from the seed of milk thistle can be conducted using hexane, petroleum ether, methylene chloride or other organic solvents via continuous liquid - liquid extraction. Lower boiling solvent will facilitate solvent removal from the final extracts.
See references:
Batch solvent extraction of flavanolignans from milk thistle (Silybum marianum L. Gaertner). Wallace SN, Carrier DJ, Clausen EC. Phytochem Anal. 2005 Jan-Feb; 16(1):7-16.
Extraction of nutraceuticals from milk thistle: part II. Extraction with organic solvents. Wallace SN, Carrier DJ, Clausen E. Appl Biochem Biotechnol. 2003 Spring; 105 -108:891-903.
Silymarin extraction from milk thistle using hot water. Duan L, Carrier DJ, Clausen EC. Appl Biochem Biotechnol. 2004 Spring; 113-116:559-68.