Today's cassette repair was just replacing a felt pressure pad. The glue that holds them to the metal spring tends to fail eventually, and they fall off. This one came off very cleanly, so the repair just involved pulling out some tape to get better access (best to do this with the leader rather than the magnetic tape, as it's harder to damage and less of a problem if you do), cutting a small piece of adhesive-backed felt and putting it in place with tweezers. Tape sounds good as new now!