been told if you change it completely it will damage the automatic box so don't know what to do
I know its not a 7 speed box think its 5 its a 2005 e320 w211 automatic 3,2 engine
Who told you that? You should completely drain it out but even then it will have some old fluid in the system. If you want it all out, it needs flushing.
Hi Op. This subject is covered all over the internet and on this forum. If it is the 722.6 5 speed box it is the same one found in all sorts of vehicles including trucks, it is a very robust piece of kit... if maintained correctly.
Go to a gearbox specialist or MB independent and pay the £200 or so that they will charge for an oil and filter change .
If done properly the oil in the torque converter and cooler pipes will be drained at the same time, around 8.5 litres in total.
As the above post, it’s not worth all the hassle changing it yourself. I paid £181 for my SL350 Job done by local MB Independent and included new electrical connector seal which started to leak.