From the info given in this post so far I would guess ethanol in gasoline reacted with something.

The stringy stuff you saw on your fingers is some kind of “polymer”

Maybe ethanol+water+bacteria+fungus+ “God only knows”

Both bacteria and fungus make complex “Biofilms” that are goo-like.polymers.

Save samples of the stringy goo stuff.
Buy a bottle of “Starbrite Star*Tron enzyme fuel treatment”

Put the goo sample in a glass jar,
cover it with Star*Tron liquid
and see it it dissolves some over time.
Maybe also send a sample to Starbrite company.

You could send a goo sample to Oak Ridge National Lab in TN and ask that they forward it to the employees there that wheel dyno test vehicles at Oak Ridge for the EPA and have it identified, perhaps using the xray diffraction equipment that they have in abundance at that site.

Last suggested step:
Eat a large portion of the goo.
If you die Corner will order a Toxicology report.
Ask your family to post this report here on Moparts.