If your transmission shudders a little and or hesitates between shifting from 3rd to 4th then it is probably your B valve(parts are 100 dollars)and depending on the MB model often can be done without removing the transmission......Many people listen to transmission shop owners that do not know much about Mercedes transmsissions except they will tell you it needs to be rebuilt...You would be wise to change your fluid and also drain the torque converter(very simple), change the filter, install a new gasket and refill with mobil 1 tranmission fluid(5 dollars a quart).....I have also used transX and it does work....I have added it to mobil1 ATF....I have never seen many american transmission last 2-300K miles...And I have had a number of MB's that have 200-300K and the transmission is still working...The return temp of the trans fluid is about 150-160 degrees depending on the model....I have never wondered about the trans cooler as much as I have wondered about the oil cooler...Jim

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James A. Harris