It's been a little time since you joined and the post that I have just seen, seeking advice on the hydraulic leak on top of the hydraulic oil tank. I do apologize for my slow response and, more than likely, someone else would have provided you with a solution to your query. There are three areas where you can get hydraulic leakage. One is from the large nut that can be a little difficult to undo, and one can also get leakage from the Allen headed bolt. More than likely, that is not your problem. Strange as it may seem, most of the time leakage occurs on the joint where the Pressure Regulator is bolted to the tank.
You'd think that it would be impossible to have a leak in that area, considering that its location is right on top and and the correct oil level is always down towards the small filter area. However, if your gaskets are faulty, a leak will occur. Mercedes has chosen a somewhat spongy special seal to seal that area, and replacement of that seal if new, and available, should solve the issue. I suspect that this seal may no longer be available - it is really quite special. I have, with some success, fitted a replacement 'O' ring, but it is tricky and important to get the correct size. When removing the Pressure Regulator from the top of the tank, you will note a portruding edge right around the opening. It is important that any seal you purchase must not seat on top , or near that sharp raised edge - it must sit just OUTSIDE all the way round, and the 'O' ring must also fit snugly inside that metal base that is attached to the Regulator. There is also a large 'O' ring that becomes visible when you unscrew the spring retainer attached to the bottom of the Regulator., and that perhaps may also create the leak.
Anyway, it's all a bit long winded, but patience and the correct or suitable seal should stop the leakage of the hydraulic fuel. Regards Styria
6.9 hydraulic.jpeg
