I’m still working my way through this, and after some discussions on the forums a member called OM613 advised me to place a filter before the fuel got into the high pressure diesel pump, but it looks like there already is one, and it’s called a Pre pass filter.
Checking this document from Mercedes mine is the one on the left.
It took quite a while to remove as the fuel hoses did not want to loosen and in the position that this is, it’s very hard to get a grip. You need a 10mm spanner to remove the screw (the screw attaches the pre pass filter to the engine bay). In the photo below you can see the filter bowl and butterfly screw, it wasn’t too hard to free once i squirted some WD40 on it.
Once you loosen screw 52 you can get more access to the Pre pass filter and the hoses.
as you can see it’s in a state (like everything else in the engine bay..), but after perseverance I got it out eventually. The spanners shown are what you’ll need to remove it. (19mm to get a grip on the pre pass filter, 14mm for the fuel hoses/tube on either side, 10mm for the screw).
I gave all the parts a good cleaning and am looking for replacement filter/seals…
closeup of the filter housing
and it’s all put back together again while i search for replacement bits.