What does the condition of the hydraulic fluid have to do with the 12th August accident? The control rod came undone, doesn't matter how clean or dirty the hydraulic fluid was, or how full the hydraulic module reservoir was, once that control rod comes undone it's game over. As a matter of thoroughness I guess all the fluids would get tested as part of an accident investigation. In the S76 the hydraulic pressure filter is not a bypass type, so any dirt should remain on the upstream side of the filter until eventually the filter gets totally blocked with the accumulation of further dirt. Unless of course the source of the dirt is in the servo, which if it is making particles then you're potentially in a spot of bother. The hydraulic filter on the downstream side of the servo is a bypass type, but that is for a different reason (you don't want that filter blocking because the pressure across the servo will equalise causing the piston to lock).