Great to hear you fixed it. BTW was it suffering sharpness wide open at specific focusing distances? The rear cell must have totally came loose for significant rattling to be heard. Additionally, and depending on lens design, a slight shift of the rear group away from the front group usually just results in a nominal change of focal length that tends to be compensated for when you check focus through the viewfinder. This is why it's not strictly important that the tightening of the real group isn't exactly as it was at the factory - as focusing shifts the front away from the rear anyway. That's why I ask if this was only present at the limits of focus or if the rear group was completely unthreaded. If its the latter I'm surprised you got sharp images at f8.
Stop worrying about grain, resolution, sharpness, and everything else that doesn't have a damn thing to do with substance.