A couple of months ago I found an Onkyo double cassette deck at a thrift store. $10 and in really mint condition. I have several sealed, unused and stored at room temperature metal cassettes, Realistic/ Radio Shack and Maxell. They have to be somewhere between 20-25 years old. I meticulously cleaned and demagnetized the deck and treated the rollers w rubber restorer. I played one prerecorded cassette that I picked up and it played fine. I even recorded onto a cheap type one tape w no problems. When I tried two sealed Maxell and two sealed Realistic metal tapes the deck kept shutting down and what recorded was warbled. Examination of the tapes showed ripples and waves on the tapes themselves. I’ve purchased some Maxell types 2’s off EBay. These type 2’s have to be around the same age as the metal tapes that I’ve had to trash. Should I expect even sealed nos cassettes to be prone to rippling, waving, etc? Are metal tapes more apt to deteriorate over time? I wouldn’t mind fooling w the deck and making a few mix tapes, but the prospects don’t look great. Any thoughts appreciated!