Shortly after switching to e85 my fuel level gauge started drifting. Typically it'll start reading normally, and then quickly fall to empty as I drive, typically in a matter of 5 minutes or so.

I don't know if it's related to the e85 switch or if it's just a coincidence. Are there any known material compatibility issues with the stock FD fuel level sending/measuring assembly?

 

I haven't seen any material failures related to E-85. I have had E-85 in my car for two years now.

Possibly a coincidence.