Try WD-40 or Break Free
Probably too late for you, but maybe others can benefit.
Recently I've had to free several nylon zippers with corroded aluminum slides and pulls. They were on diving equipment bags that had been unused for years. The first ones were large and we managed not to pull apart the floppy thing from the slide. It took patience, so as not to tear it off, and we even gave up for a week or two while it soaked. Next time, and using more lube (Break Free), it worked. It might help to grab the slide piece, not the floppy handle, with pliers. We were scared it would tear, but this time it didn't.
Next time was with much smaller zippers, and even though we did pull one handle off, we were able to grab the slide and eventually make it work. WD-40 was used here.
Break Free was distributed by Duracell and the can we have is 15 years old, at least.