If that's the original vintage Agfa bellows, and you've attended to the Agfa sludge-grease problem, I'd just replace the bellows. There is nothing to recommend about a post-WWII Agfa bellows, and if it isn't bad in some way right now, it will be in the future. If you like the camera, I'd suggest to replace it and see if your problem goes away. An issue in the first or 2nd fold toward the lens from the film gate can be hard to spot with a flashlight in a dark room-- I got foozled by a Plaubel Makina II this way, and the Plaubel is much easier to check than an Agfa.