So I just mixed a 64 ounce bottle of Flexicolor Stabilizer III to stabilize very-expired C-41 film my daugher shoots (Kodacolor II, original Vericolor, etc), and cross-processed E-6 film. Our local minilab processes it, but with formaldehyde-free stabilizer.

What's the real-world lifetime of this once mixed? Kodak's Z-131 says 8 weeks, but I bet that's very conservative, as the formaldehyde must be a rather effective preservative. I presume it doesn't grow scum like PhotoFlo will.