When changing my fuel filter I usually fill it up with atf and then prime the engine. In the tank I run Stanadyne diesel fuel additive, I have used it in my 240d's and Cummins. I noticed less smoke on startup and overall. I have seen people use 2 cylinder oil in their tank as atf has powerful detergents that have been rumored to start to affect cylinder walls with prolonged use. 2 cylinder oil has the same lubrication abilities as atf but without the detergents. Also twice a year, I do a a diesel purge using Lubro Moly product. The amount of filth that comes out of the return line is incredible.