I drove a 190E for 4 years (my personal car) and the whole time I drove it it shifted hard between 2nd and 3rd gear and I did everything I knew of to correct it. By the way it starts in 2nd gear unless you floor it. I work at a Mercedes shop and every 190 that I've ever driven shifted just like mine. As I understand your transmission is shifting hard at every shift and if that's the case it sounds to me that there's no vacuum to the modulator valve or the valve is defective.