Dear Mr. Hurlburt,
Thank you so much for posting your request on History Hub!
We suggest you begin your search by requesting your grandfather's Official Military Personnel File (OMPF). OMPFs and medical records of officers and enlisted personnel of the U.S. Marine Corps who were separated from service after 1904 and prior to 1957 are located at NARA's National Personnel Records Center (NPRC), (Military Personnel Records), 1 Archives Drive, St. Louis, MO 63138-1002. To request these records, please mail a completed GSA Standard Form 180 to NPRC.
We hope this is helpful. Best of luck with your family research!