Mercedes auto transmissions are very reliable, but as with everything mechanical, only when properly maintained!
Generally, (and also per mercedes manuals) transmission oil change must be coupled with a transmission oil filter change!
The most important things that should be observed are:
- The person dong the job should know what he is dong ( no new information!)
- ABSOLUTE cleanliness MUST be observed, the right transmission oil MUST be used (listed in the MB oil spec-sheet)
The torque converter also has a drain screw, a lot of oil flows out of there!
The person performing the job must have a proper torque wrench, cause thats the only proper way the oil pan bolts can be tightened (after changing the transmission filter). The tightening torques are in the range of 10-15Nm (which are minute) and jahil mechanics would always try to over tighten them, which would result in a deformed oil-pan causing leaks!
So my advise, if you cannot do it yourself, do not save money, go to shahnawaz if you think they have the proper expertise to perform the job!