Ampex 407 analogue tape had an issue in c. 1975 with the chemical composition of the glue that held the magnetic oxide onto the backing tape…
So when you played the tape, the oxide started to come off and the heads and the rollers started to gunge up and the tape would disintegrate. Every time you played it, you lost a bit of signal, mostly high end.
so…
the solution, and the recipe:
Bake the tapes at 50ºF for 4 days continuously, which solidified the glue.
after testing, 3 hours at 50ºC (fan oven) was sufficient, providing it was played within a couple of hours… which is enough time to master the audio.
So I would set the oven on auto to turn on at 3am and load the tapes in the oven (ex-box) before I went to bed. Arise at 7ish, breakfast, shower, start mastering at 9am when they had cooled down…