Had a situation last week on a new-version 738 with the articulating seats in F. A woman in the row behind me could not get her seat to recline. FA had no clue, but asked the captain to take a look. He easily fixed the issue by removing the seat cushion and bending a tab on each side back to it's normal position. Just after takeoff, I discovered that my seat had the same issue. The FA had paid attention to what the captain did, and performed the same maneuver on my seat. If you end up in F on a new version 738 in a seat that won't recline, make sure to ask the cabin crew if they can fix, or (if not) see if the captain knows what to do. Obviously, it would be much better to discover on the ground than in the air. It's a one minute fix, if it works.