Tallsandwich - here's a posting I made on the subject elsewhere on the forum. Hope it is of use to you............
I don't know if this will help the debate, but here goes. In my day job, I was involved in an investigation into a 747 uncommanded elevator input a few years ago, and also in the 737 rudder system redesign conferences in Seattle.
The cause of the 747 elevator deflection was a combination of two things - a bit of grit in one of the selector spools on the tandem actuator preventing full closure, and return lead rather than return lag on the other spool. As the design of the 747 elevator and 737 rudder PCU's are almost identical, this caused a light bulb to illuminate over the head of one of the development engineers, and much finger pointing ensued towards the 737 actuator.
Parker Hannifin have redesigned the spools to prevent return lead, and have increased the overlap margins to make some allowance for contaminants in the system.
Mr. Boeing has redesigned the entire system; the only salvageable bit is the standby actuator. Even the yaw damper coupler is different, as is the wiring and the magic boxes. There is a redefined hydraulic limiter, and a mechanical limiter.
The Speed increase was an attempt to ensure that the aircraft operated above crossover speed and so give the pilot a fighting chance at controlling it if the rudder declared UDI. I don't know much about flying 737's, but from a systems perspective I'd suggest that as the 737 has manual reversion, the best course of action in the event of a rudder hard over would be to dump the hydraulics and fly manually.
Other Boeings have non return valves in their systems to prevent the wobbly bits flapping around in the wind in the event of a total hydraulic fluid loss; as the 737 has manual reversion, that would be a bit of an own goal, so it is quite normal for the control surfaces to move about in the wind, whereas it would be a bit worrying if a 747, 767 or any other true Boeing flying control did so.
I'm now sitting back and awaiting the inevitable character assassination..............