What is your end goal? Will you be happy just finishing a marathon or do you need/want to do it in a certain time.
Assuming you feel fine up until the 8th mile, maybe try running with a compression knee brace. I bought a cheap pair off Amazon a couple years back and it has been a game changer in dealing with my knee pain. Maybe try to run 14 miles with that this week and see how you feel as you run and go further if you can. No matter what, you need to dial it back after this week.
Here's what I bought: https://www.amazon.com/dp/B01NBMVZ67/ref=cm_sw_r_cp_apip_YLfLE3BAM1jii