I've spent all day with my cassettes! I won a huge auction on E-Bay for around 125 recorded on once, (well according to the seller, but all of them are in excellent condition, tapes & cases). Included were Maxell XLII90, XLII100, XLIIS90, XLIIS100, TDK SA90, SA-X90, SA-X100. I paid next to nothing for all of these. The tape gods were certainly smiling on me that day.
I have a commercial/professional tape degausser that came out of a recording studio, that does a fantastic job at cleaning these up.
I'm now on my third recording of the day. So far these have been perfect. Hopefully most will be the same.
Boy, I sure love this. Hands on and very rewarding. What a BLAST!!!