Little update,I did a test on the system(home made ).
I filled a bottle with water,and removed the hose that goes from coolant tank to overflow tank.Then I put a hose on the neck of the coolant tank and in a bottle with water.I heated the car to operating temp,drove it,let it idle,then i rev it and...there is no bubbles in the bottle!So even if there is a gas leakage in the cooling system it is still not that big,and it does not open the rad cap (i have a 120-1,2 bar cap).
So I will drive it as is,and I will update if something happens .

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Mercedes W140, S350TD, 95.
Mercedes W140, S350, 92.
Porsche 944, 86 N/A.
Porsche 944, 85 N/A automatic.
Porsche 944, 84 N/A.
Porsche 944, 83 N/A.
Opel GT, 73.
Toyota Supra MA61,84.

New update,I decided that it is time to take the head off,and what I found is that between cyl.no.5 and 6 compression was getting in the coolant line.The head was warped so I took it to my cousins machine shop.After new gasket and machining the head no more hard hoses .

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Mercedes W140, S350TD, 95.
Mercedes W140, S350, 92.
Porsche 944, 86 N/A.
Porsche 944, 85 N/A automatic.
Porsche 944, 84 N/A.
Porsche 944, 83 N/A.
Opel GT, 73.
Toyota Supra MA61,84.