Several Years ago someone had the same issue and pretty much got the same response as marturo said.

If thinges get desperate I uppose you could remove the Power Steering Pump to get a better position and leave the Hose Nut screwed on loose while you re-install it.

Are these Real Mercedes Hoses or are they aftermarket Hoses. If they are Aftermarket it could be a host of issues including the wrong threads.

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84 300D, 82 Volvo 244Gl Diesel