Hey Ian, during your DeVere head-flying-through-the-ceiling purchasing mishap did you happen to damage the bellows at all? The bellows on my 504 looks like it might have suffered through it at one point in it's life. I'm not a 100% sure though. Anyways, the problem is that one of the top corners of the bellows has pulled away from the bottom of the negative stage allowing light to leak past. It's not the end of the world and can be masked, but was curious if you knew how to reattach the bellows to the head entirely and what method it's secured by? From cursory inspection it almost looks adhered, but I can't really tell. I did remove the aluminum top plate where the holder slides on top of but there didn't seem to be a lot of access to get to the top of the bellows.
Stop worrying about grain, resolution, sharpness, and everything else that doesn't have a damn thing to do with substance.