Nostalgia!!! I had this problem a number of times. Had my way to fix them. If only clean folds were there and no actual wearing off of the oxide part, then they sounded ok after fixing the problem.. And yes, it was fun. I am 50 now, and still proudly possess at least 1,000 cassettes, more or less all of them in good working condition. All the best from Kolkata, India.
Your correct. It never sounds as good, but this is a way to at least hear something. In the case where it's a personal one-of-a-kind recording, it's better than losing it altogether. Thanks for your input. :)