I have lost my F3 sensor protecting cap which goes on the original E-mount (not the PL one) and I'm hoping someone can direct me to what this part is called or even a link to buy one on Ebay etc. I'm not looking for a lens cap, but the insert cap that fits where the lens inserts into the mount for protecting the sensor during times when no lens is mounted.

Wouldn't that just be an e-mount body cap or rear lens cap?

F3 is an FZ mount, not a Sony E-mt. E-Mt is FS100 , FS700 and some (all?) NEX cameras. F3 mount is same as F5, F55, F65 etc.

The F3 doesn't come with a body cap. It ships with the PL mount attached to the body. The PL mount has a cap. My F3 did not arrive with separate FZ mount a body cap. Only a PL mount cap.

This is what I am looking for:
MACHINED PL MOUNT BODY CAP | RED Digital Cinema store (US) (http://www.red.com/store/products/dsmc-pl-mount-body-cap)

not this:
REAR LENS CAP, PL | RED Digital Cinema store (US) (http://www.red.com/store/products/red-rear-lens-cap-pl)

I just have to keep the PL mount on the camera instead of off. Thanks for the suggestions.