I have this Canonet which I bought off eBay. Its very, very clean and the meter works and all that, but the aperture blades were slow to open back up. It would stop down just fine, but would only (reluctantly) open back up upon advancing the film lever once or twice. I opened up the lens and tried cleaning the blades with a bit of rubbing alcohol, and that only seemed to make it worse. Now they're even stiffer. Any tips?