Guy,
I just looked at your photos. I hate to be the bearer of bad news, but there is a good chance your sills are rusting inside out. I noticed in the photo of your rt fender the end of the castle rail has rusted away. That happened to my B too, it's bad news. I would have it checked out. The sills are the major load bearing support structure of the MGB and unfortunately are prone to the tin worm. Once it gets inside, it eats the B inside out. My outer sills were replaced sometime in the past, and the inner sills were poorly patched. On my car, now that patch has started to rust out. Not good. I'm the in the midst of a full sill replacement. Not fun.