You can also put the 72 pin connector in boiling water for like 30 mins, take it out and let it cool. That should reset the pins back to "factory condition"

If your socket is the unreliable part, I've found that getting a game fairly wet on the contacts with isopropyl alcohol and then repeatedly inserting/removing it will get the slot nice and clean inside. I usually blow it out with compressed air after that.

I did that this weekend. New connector cost me ~ $15 AUD off an ebay store.

Took me a bit longer than you but I was being super cautious having never opened a console before.

Highly recommend for anyone else with a broken NES lying around. Good chance the 72pin connector is at fault.