w208clk320 brake have intermitent problem of loosing pressure, soft and to the extend that while braking , it loose press and pedal went down no brake but when pump regain the braking!

First of all, this is the W209 forum and you have a W208, so you might get better responses from that forum. However, the brakes are pretty much the same, so it's not a big deal. Check your brake fluid level - if it's low, then you have a leak somewhere. if not, then it's bad master cylinder.