Somebody plz help me on this one, I have yet to purchase any MB manuals and I'm getting conflicting info from local dealer.

81 300SD 126:
I checked my trans. fluid last week and it was below the first bend in the dipstick. I proceded to add 2 litres. I checked it again this week and it's still below the first bend. Strangely the level shows the same regardless if I check it in idle (after shifting thru gears) or with the engine off. What's the capacity of this tranny? What level is healthy? Thanks in advance for any help.