FOLLOW UP
Just to close this one, there is always a reason for oil loss of course. So after 3 top ups the garage found it, admittedly the top ups are only less than a cupful.
I had the plastic undertray off and cleaned, then ran for 500 miles. Off again but no evidence of leak so top up power steering fluid. Another 500 miles and steering was graunching again so back to indie.
They managed to see a small amount of oil on the air con condenser face behind a fan.
The power steering fluid is cooled in the top couple of rows of the condenser rad, obviously isolated from the air con fluid. A replacement rad fixed the problem.
The real warning here is that Merc in their wisdom fitted a dual pump on this model (and others with ABC), one side powers the steering and the other the ABC suspension.
If one side fails through lack of oil the pump is history and expensive to replace as it is dual function. The ABC system will also then need a Star "Rodeo" work out to purge any air out. By regular top ups I have managed to save mine, mainly because the groans from the steering indicated that all was not well!
So if you need to top up anything regularly make sure you know the cause of the leak.
This rad was covered by a cowl at the top and has an electric fan bolted to it so it is very difficult to inspect without stripping them off. Who would have thought that the steering fluid needs cooling? I guess it is because it gets a lot of heat transfer from the integral ABC system when it circulates oil. Both reservoirs for steering and ABC are also independent.
My original Behr rad was an all aluminium job and the leak was inside one of the thin pipes inside at the top middle, no physical damage and the rest looked like new apart from the flies stuck on the oily fins.
Don
