I have towed with several Mercedes and have never fitted a gearbox cooler. I have always assumed that if the book says you can tow X Tonnes with no asterisk with a note saying you need a cooler to do this, then you don't need one. Or check with the dealer
I currently tow a Bailey caravan 1300kg ish with my B180Cdi, no problems.
I have always assumed that if the book says you can tow X Tonnes with no asterisk with a note saying you need a cooler to do this, then you don't need one.