I am still a little confused about which transmission our 1988 300TE has.
722.4.... or is it a 722.3?

Car has 69k on it now and the fluid color "looks" ok, but as we have no records we dont know when it was changed last.
Shift fine about 98% of the time, but I have noticed a slight slip on the change from 2 to 3 when cold.
Previous owner gave us a filter and gasket and said they had planned to do it.

What fluid should we use... MB only... a Synthetic like Mobil 1 ... or just a good quality normal fluid?

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2009 Mercedes ML320 Bluetec