The problematic are on the turbo drain is grommet and O-ring at the base of it. There is an O-ring mid way between the upper and lower tubes but it is higher then the oil level and I have not read of it leaking.
There is also a little nipple with an O-ring in the same area for the Air Filter Oil Separator.
http://www.peachparts.com/shopforum/diesel-discussion/113087-w126-om617-1985-300sd-turbo-drain-tube-gasket-seals.html
Note that mine has some rear main seal leak but in general the rope type rear main seals don't leak anywhere like a 30 some year rear main rubber lip seal would.
Do you think are having any sort of excessive crankcase pressure?
You don't need the new tube unless the one you have gets damaged:
http://www.peachparts.com/Wikka/OM617TurboDrainTube