Big fan of Golden here too! I’ve used mine diluted with distilled water, and haven’t yet had any trouble with the paint “breaking” or degrading over time (my oldest PYO is coming up on 5 years old). But the GAC 100 is much nicer if you want to dilute the paint in something that will still cover the piece. The super-thin layers you get with water are only useful if you plan to do a whole lot of layering.
Enjoy these paints–they’re wonderful to work with! 8)