Sorry guys, its the -300 series.
I definitely have 'speedbrakes extended' checklist as well as 'speed brake do not arm'.
Rudder going to high pressure is referenced in Vol 2 flight controls (page 9.20.10 ).
Staes hydraulic pressure returns to normal when descending thru 700' when N1 difference between left and right exceeds 45% and if B hydraulic sys depressurises. Can't see the logic of JUST B depressurising............