Epson Ultrachrome inks have faded horribly
Concerning the plasticisers, I suspect almost all plastic tubes would have them. White tubes are often PVC, and a tube that is not entirely rigid is likely in the polyethylene family. Both kinds resins would use plasticisers in their compounds.
Curiously I have an A0 print I made in 1992, which has been on the wall since then, and it has gone a touch orange. Reading these posts, I realised that it has gone more orange. It was a low res file, and the printer (which I was testing) would have been using dye inks, because I don't think they had any other types back then. This was just the beginning of the poster market etc. market. It was compared to today a low resolution printer, I suspect it was an HP one actually, I am not sure about Epson back then.
I guess I should find the original file and get it re-printed.