Agree with the need for a good scan (I am not so dogmatic about SDS vs carsoft vs Autel though).
No offence intended here, (and I'm sure there wasn't in your post either)
I'm not trying to be dogmatic.
There is pages and pages of very good reasons to spend circa £400 on a basic SDS System, not just the ones written by me either, so yes I do plug these machines, simply because myself and others who have made the transition to SDS from lesser machines are not exaggerating claims
An icarsoft may well tell you that your PSE or TCU is faulty, but it won't be able to Version Code a new or used unit to suit the specific vehicle, many owners have ended up chasing ghost faults because they do not realise these cars (even the aged R170) are as complex as they are
Being a Garage Workshop owner who specialises in Diagnostic and Rectification works, and for the best part of my mid 20's to early forties I owned and ran a successful Auto Trans Rebuilders, I have the luxury of many Dealer Level machines as well as 3 generics, Snap On, Autel and Delphi. These Generics obviously cost way north of the SDS £400, and are very good in their own right.
No one machine does all unless you have the Dealer Level Kit, like SDS for MB's, JLR for Jag Landrover, ISTA INPA etc for BMW, VAG Com for VAG Cars etc etc.
I know for a fact that icarsoft and Autel / Snap On / Delphi and many more do not access more than 80% of Codes and not in all modules.
I have often experienced owners going off on tangents and telling me there "is no fault codes", plug the Car into SDS and wham Fault Codes, Data, Guided Diagnostic, Wiring Diagrams, Part Locations, Part Numbers, Version Coding, Developer etc etc etc all at your fingertips.
These are just a few reasons I advocate using a £400 SDS over any other, simply because it is the correct and very powerful tool for these Cars, and not
just a simple diagnostic machine
I'd go so far as to say it is almost essential
on later Mercedes models, such as R171 , R172 and also on same vintage as R170 but higher end Cars like W220 S Class C215 CL etc etc
Anyway, like I said, just a discussion of what and why from my own perspective, absolutely no offence intended or taken
Back to OP
I agree this does sound like a low Oil level, but it could also be a bunch of other things and I know for a fact if it were put on SDS I would know exactly where the fault lie in the Transmission System, and whether or not it was worth a rebuild or good used unit time
If it had been "read" on anything else one simply cannot be certain, unless it is one of the more common faults.
So first and simplest step, verify the Trans Oil Level and correct if necessary. Check the areas mentioned for leaks, plus look for other leak sources if level is low.
If you need to add Oil, once the level is correct, then test drive and report back if she's driving OK, if so rectify leak, if not we need to go more in depth !!
Final thing to note is that each time you add oil, it clings in the dipstick tube, more so on MB 722.6, so you need to insert and remove/wipe the dipstick a few times each time you add oil in order to get an accurate reading
HTH, Cheers Dave