>>11594580 (OP)
If I had to guess it's because the gi vest is made of a softer white plastic that's made from a chemical curing process rather than strictly being heated and injection molded, and the plastic didn't fully cure and years later it started separating and "sweating" out chemicals that damaged it. If you took it out of the box it would probably feel really sticky. The same thing supposedly happened to some Saruman figures from the Lord of the Rings 6" line, the affected figures became sticky and covered with a gross residue years later, and just like that Ken figure they had a lot of flexible white clothing pieces.
If you're an in box collector you can't really do anything about it. Just leave it and accept that it's a less than pristine example. If you're an out of box collector you could try your luck with cleaning the affected piece to get rid of any sticky residue and then paint it, or replace it with a cloth one from eBay.
