Kurt said exactly what I was going to say. We just had this discussion on another forum and the poster said he called a fuel tank maker and they are no longer making tanks from Poly because the ethenol is eating them up.

We were seeing lots of this in the marine repair industry I worked in, ethenol was eating up fuel lines, plastic tanks, and even aluminum and steel tanks were being damaged by it.

I would bet that is what you have going on.

Don