Mecedes W210 autobox woes

First check what level is the oil at. Do you have the dipstick for the autobox as I know some mercs just had a blanking plug and the dealers had a dipstick which they charged an arm and a leg to use!

Check the vacumm lines going down to the gearbox.

OK i had a few companies try to tell me my gearbox was shot ...has 56K ..... check to see if you have a vacuum modulator on the side or somewhere on the gearbox. It has a rubber vacuum hose coming off it. If you find it pull off the hose and see if there's any gearbox oil in it at all. If so ..you modulator has gone. They control the gearbox pressure. It sounds a little or a lot like ''low pressure '' in the gearbox possibly.The modulators have a diaphragm inside which after time go. Oil in the pipe is a clear indicator or using gearbox oil when you don't see any leaks.... ''burns out hrough the engine etc unnoticed but maybe white puffs of smoke on occasion'' ... if you have that change the modulator ''BUT'' ... don't lose the pin taking the old one out. You'll need it. Just asking .... in reverse does it judder at all??? Defo low gearbox pressure if so. Also the clutch bands maybe stretched or need adjusting ... maybe replacing due to slipping. But check the vacuum line as said first off the modulator on the gearbox ... may help you?
I changed mine and at the same time done a gearbox flush with approx 12-15ltres of oil ...then just cleaned out the sump....new gasket and oil and sorted...smooth as silk :-). ... could even do a flush and oil / filter change. You should have cooler pipes from the gearbox ''possibly'' to the coolant radiator ...its normally the upper pipe. Turn off your engine and loosen the pipe if there is one ''don't know mercs'' ... get a funnel and large container then lower the pipe into it. Start the engine and tick over.....let the oil pump out until it stops add a bit more then turn off your engine. That should clear curse word out of the torque converter etc... then do the rest oil / filter / gasket and see.