Re: as the decade comes to a close. so do tapes
Cassettes were particularly susceptible to 'melting' & rot, but they can often be brought back to life with baking, long enough to re-record into your favorite digital format (mine is still standard CD, 16/44.1)
Baking tapes isn't as mysterious or difficult as it may seem, and it can be done cheaply and quickly.
Get a Mr. Coffee Food Dehydrator at your local thrift shop for about $5. Any dehyadrator with a fan will do. It should have all the trays inside, and a lid.
Take the tapes out of their cases and place them on the uppermost tray. Run the dehydrator for 30 minutes. And that's it! Reels can be handled the same way. But only use the top tray, don't attempt to load the entire dehydrator.
You may then transfer the tape with little or no problem, playing it 2 or 3 times if necessary. I've fixed and rescued many hopeless tapes in the past, and this cheap, fast method absolutely works. Considering a toaster over or other extreme heat devices is asking for trouble and melted tape and plastic reels/cases.
Also, it's a good idea to make a few copies of the material. CDs/DVDs are cheap enough, make two and be safe.