Most of the times, the only thing you need to repair to fix random key-presses is the soft plastic under the input-board connector to the motherboard.
At step 6 just move the motherboard upwards and you'll be able to see the connector.
Take the black soft-plastic-thing under it, and make it thicker with some tape. ( roll some tape around it 3-4 times - cut the tape properly so it can fit afterwards )
Now put everything back.
Random Presses are gone. Both of my controllers had this problem after a few hot summers and many hours of gameplay... both are fixed now.