I first noticed something wrong when playing super mario world.
I had to hold the left point of the D-pad down Very hard.
This made moving quickly impossible.
So I took it apart, put it back together.
Now both Left and Down behaved poorly.
Repeat. Down is fixed. Yay! Left is still crap. boo.
When I took the whole thing apart and tested it the board was good in all respects. I did not have to push down hard at all.
Unfortunately, when reassembled the problem came back. As far as I can tell it’s flawed by design - there is a crook in the d-pad where there ought not to be one.
I’m not sure what to do beyond giving up. I bought it at gamestop used, so there is no way nintendo will replace it.