I had a similar experience, but not as catastrophic.
The plug clouded over very soon after installation and became useless. When I took it out, parts of it crumbled off.
I don't have the plugs sitting in front of me, but right on the package it states something like: "Not for long-term use. Use only for setting float level." Obviously Holley knows that those clear plastic plugs can't stand up to the solvents in gasoline.
As for the needle & seat deteriorating, I wouldn't use any old (rubber) ones that have been sitting on the shelf a few years. All rubber dries out over time, and stuff made prior to a few years ago might not work with today's fuels. Also, they do make all-metal needle & seats. Might not be a bad idea.
