Chosen Solution
While dissembling my iPhone to see if I could revive it from a splash of sea water, the little square foam patch that covers the top of the antenna plug next to the battery connector fell off and disappeared. What is this material made of? What can I use instead? See step 27 of the iPhone 5s logic board replacement guide.
Don’t worry about it. That thing gets loose all the time and I never put it back on phones.
