There is also the possibility/probability that the addition of the Split Scimitar winglets has had an adverse effect on the wing bending loads carried by the pickle forks.
Apparently the spanwise lift distribution has shifted the centre of lift further outboard on the wings which would necessarily give rise to greater wing bending loads at the wing attachment points from both static flight and gust loads.
Possibly those B737s that were designed from the outset to have Split Scimitar winglets might have strengthened pickleforks to account for the increase in bending loads.
But those B737s (eg, 800, NG) that were fitted with the after-market mod Scimitar installation (without beefing up the wing attach load path design) would necessarily suffer a reduced wing attachment fatigue life due to the higher loads imposed by the addition of the Split Scimitar winglets.
Perhaps more engineering learned members than I might like to comment?
