I replaced the B2 piston and I still have the flare issue when shifting from 3 to 4. I disconnected the vacuum modulator and capped the line and I did not get the flare. I was able to adjust the modulator (turned clockwise all the way in) and it helps somewhat. I really don't know what else to try except check the B2 band adjustment. Mercedes dealer closest to me (1 hr away) wants $3K to replace the trans. thye are offering a 2 yr unlimited mileage warranty. No trans shops close to me have any experience with Mercedes trans. Also thought about checking the governor to make sure its functioning properly.