Mtro

I was discharged in 1975 from CampPendleton 1stMarDiv. I have recently sought disability due to a knee replacement that is service connected. Although was unable to complete the claim because my military medical records cannot be found. Tried contacting the unit I was discharged from and also the hospital that I was treated at. No one can find anything. Could someone provide any direction or ideas? The only thing that can be found is my entrance physical. Thank you