I just bought a crown graphic. beat up, but all the working parts are perfectly fine and the lens is great. though the ground glass and the fresnel are worn....marks and scratches. i'm new to this 4x5 stuff, and was wondering how i go about cleaning and/or replacing the ground glass and fresnel? are these easily replacable?

Remove the back. Both pieces are held by two clips, one on each side, held by a screw.

Clean the ground glass and fresnel with soap and water. Be careful, the thin glass is easily broken. Of the two pieces the ground glass is easily obtainable, the fresnel isn't.

Just make sure you put it back together correctly. The grooves of the fresnel face the etched side of the ground glass, and the fresnel is on the lens side.