I have a leak in a cooler line in transmission, put fresh transmission fluid in but problems with something slipping and stall coming from stopped position and going up an incline.

Probably a damaged coupling or badly worn pipe.
If not too late, replace the lines and refill the transmission with Mercedes Transmission Oil.

First thing to do is check the transmission fluid level and check for leaks. If the transmission is very low on fluid, for example a cooler line broke, it would cause this situation due to no pressure. If you do not see any outside leaks, but transmission fluid is very low, check your radiator overflow tank, if it is overfull and milky, this would mean the Trans cooler that goes through the radiator is leaking fluid into the coolant system.

OPPPSSS.. he hooked a transmission line to a heater core line or vice-versa //.. Get a new mechanic!!

transmission slipping could be low transmission fluid level or need a transmission fluid and filter change.if transmission fluid was real low check for transmission fluid leaks around transmission oil pan gasket or fluid leaks around cooler lines or torque converter shaft seal. if you getting steam inside cab.your heater core is leaking.if transmission fluid level okay and filter been changed could have faulty over drive switch.

Nope, no positives. It does sound like the pump has failed. If the stop leak didn't help seal any internal seals that may have failed, it looks like the transaxle will have to come out for repairs or another replacement.
I don't think the torque converter ever makes noise when bad.
I would think your diagnosis of a bad pump is correct, given no movement of fluid in the cooler lines. Kudos for checking the lines-cool idea, I never thought of that.

IF TRANSMISSION LEAKING WHILE RUNNING LEAKING AT TORQUE CONVERTER SHAFT SEAL OR TRANSMISSION COOLER LINES GOING INTO RADIATOR LEAKING.YOU WILL LOSE MORE FLUID AT COOLER LINE BECAUSE TRANSMISSION UNDER PRESSURE THE OIL PUMP PUMPING IT THROUGH THE RADIATOR YOU WILL LOSE ALL YOUR FLUID QUICKLY IF LEAK COMING FROM COOLER LINES GOING INTO RADIATOR.DONT DRIVE VAN UNTIL FIX BECAUSE FLUID LOST WILL BE TRANSMISSION LOST.

CHECK UNDER VECHICLE IF TRANSMISSION FLUID UNDER TRANSMISSION MORE LIKELY PAN GASKET LEAKING FLUID.IF FLUID HAS NOT BEEN CHANGED THE PAN GASKET GET HARD LEAKS FLUID.THATS IF YOU HAVE SLOW LEAK.IF YOU LOSING LOTS OF TRANSMISSION FLUID ITS .LEAKING AT TORQUE CONVERTER SHAFT SEAL.LEAKING AT COOLER LINES.CHECK COOLER LINES FROM RADIATOR TO UNDER CAR WHERE COOLER LINES GOES TO TRANSMISSION. AND CHECK LEAKS AT FRONT DRIVE SHAFT AXLES SEALS

Good Evening. Unfortuantely there is no easy path to a right answer here without removing the skid plate. In front of the engine are transmission cooler lines and other miscellania. The best advice i could give you is take down the skid plate and have a can of brake cleaner handy to clean everything off while you have it turned off then have someone turn it on for you so you can visually see where it is coming from. Hope this helps and if you have any more questions feel free to ask.

It sounds like the Transmission line has a leak. Check the transmission line from the transmission to the radiator. You have two steel lines which runs to and from the transmission to the transmission cooler in the radiator. The line could be corroded and may need to be replaced, good luck and service the transmission too. The transmission on the transport are know to have problems when ran low on fluid or dirty transmission filter.
Good luck and hope this helps.

Ok the transmission is gone anytime a transmission slips between gears its bad and the worst thing you could have done was change the fluid and filter because the only thing holding any friction on the clutches was the old fluid once you drained the old fluid and added fresh you washed the last remaining particals of clutch material off and now the transmission is totally dead. you need to replace the transmission, torque converter and flush all of the old fluid with clutch particals from the transmission cooler and lines use air and brakek cleaner to blow out the debris from othe transmission cooler lines do it from both lines first one then the other line until no more junk comes out o it will "kill" the replacement tranmission.
If you find this information helpful please give me a fixya Rating and if you need any further help on this problem dont hesitate to contact me here or at [email protected] Thanks. Randy