Well I had my brand new, literally out of the box brand new and never used Olympus OM 21mm f3.5 MC lens delivered a couple of days ago. I had bought a very expensive Novoflex adaptor to go with it. I hadn't yet taken a single frame when the lens with adaptor attached rolls off the table and hits the stone floor. There is a tiny dent in the adaptor where it meets the camera. I thought it was indented and therefore wouldn't be a problem to the fit but I did some testing with the camera and lens today and indeed the right side is slightly out. There is a slight, 1/10 of a mm protrusion at the edge of the tiny dent. I doubt it would be noticeable with a 50mm lens and could be filed back down easily by someone more talented than myself with the right tools however I just went online and spent another £99 on a new one. Sigh...
BTW if anyone wants a DIY project, I'll sell the old one for £50, half price. It really is a tiny dent, doubt I could even show it in a photo.