I also have a 3x4 RB-D to go with this 4x5. That one's in excellent condition in every respect (barely used it would seem). The latching mechanism is completely different from the 4x5 - I wonder if that's inherent in the 3x4s or it's a function of age. Also, the 3x4 is marked as a "RB Graflex Series D Curtain Aperture" while the 4x5 is simply a "RB Series D Graflex". If you come up with a fix for your bag mags it'd be nice to see.
They're fun cameras to shoot with (albeit a little clunky to handle) and they certainly attract attention. The attached is from a Civil War Living History event (not a historically acurate camera but better than a digital)