Problem being the failure of the rudder control hydraulics identified in the 1990s that caused unwanted deflection? If that's true, it's incredible that it hasn't been fixed long long ago. I'd credit that some new malfunction has cropped up that does the same thing, yes I would. Could be a maintenance issue, could be something that can be designed out, but if it's the latter it took an awfully long time to rear its' ugly head. Hundreds of thousands of flights.
It COULD even be pilot error. I've read that single-engine WW2 fighters would dutch roll when carrying a full load of fuel if the pilot wasn't careful to be light on the rudder pedals. Could this airline pilot have made a careless move and is now covering up? All speculation at this point.
The PCU Valve was redesigned but who’s to say that a box of old inventory got found in the parts room and the current Parts Crew/Assembly Line Crews may not even know about the original problem.
Gotta wait and see.