Transmission Slipping or Flaring?
 

I have a 1990 300E w/2.6 and a 722.409 transmission. I am trying to narrow down the cause of the problem (minor or major) before I tackle rebuilding the transmission. My transmission will slip or flair in second gear and never gets to third gear. I can place the shifter in "2" and will start in 1st gear and shift to 2nd gear with some slip but will never get to third no matter what. This is my first MB and have worked on domestic cars for last 15 years. After buying manual from ATSG and subscribing to Alldatadiy.com, I have "rounded up the usual suspects". Valve body is dirty, governor is broken (I doubt it), K1 accumulator spring is too soft/hard, or temperature restrictor is missing. Before I crawl under the car for a full weekend of work, I would like some advice or opinions to my dilemma....