Omega steering - ovo
Omega 2.5 Diesel 1995 speed sensitive power steering acting up does anybody know how this works and where the control unit (relay) is located ?
Omega steering - smokie
One of the mods will move this to the tech section where someone is bound to know the answer...
Omega steering - Sooty Tailpipes
The ZF Servotronic system has a electro hydraulic converter in the power steering box, this can be removed by removing it's 4 screws (one each corner of a square plate mouted in box) and withdrawn, there is a filter screen on this which may need a wash.

the control unit is behind the panel to the left of the glovebox, I think you can remove it (its a relay) by taking off the trim above the passenger's feet and reaching up behind there, second from the bottom on the left (medium sized relay?) below a bigger one, and above a smaller one, but maybe differs with models, years etc...