-Fuel Filter w/o-rings (Mahle fuel filter, Mercedes fuel filter)
-Water separator sensor (ONLY NEEDED IF BROKEN)
-6/7/8mm or Phillips screwdriver
-Hose Pliers (optional)
-Hose line plugs (optional)
First off make sure van is off and battery cable removed (just in case, don't want the fuel pump to be turned on with key).
Next remove both hoses remembering which one does where (take a picture of it). Mine came off with an 8mm socket on the hose clamp, some may be smaller or phillips screwdriver. Remove both hoses, plug and set aside. These plugs are nice to have around for situations like this where the hose is not under pressure, but may leak out.
Next remove the bolt on the holders, I believe mine was an 8mm socket again, but some may be the external torx that are common on this engine. Once the bolt is removed the filter should come freely out of the holder. Keep in mind it is still full of fuel so you should dump it into a safe container and drain it.
Next you need to remove the water separator sensor. Be careful not to break it as it is plastic and kinda expensive. You do not need to remove the center plastic knob, that is only to drain out water. Just remove the two T25 (T20) torx screws and spin the sensor until it's tabs are free from the fuel filter bolt brackets and slowly pull out.
Once out verify it is clean and has no cracks. I removed the plastic knob to inspect the o-ring inside and make sure it will still seal well. If you do this DOUBLE CHECK that the 0-ring is back on correctly. There is a small slit it fits in, if it comes out of that slit and up towards the threads IT WILL NOT SEAL.... first hand experience.
Install the new o-rings on the outside of the sensor (should have come with the fuel filter). Reinstall the sensor and bolt down lightly as you are tightening into plastic. Reinstall the filter into the holder, reattach both hoses and clamp down with hose clamps. I would recommend checking for cracking in the fuel line also, the hose clamps can have a tendency to cut into fuel line and may be a problem down the road. Tighten down the holder at the base of the fuel filter and make sure everything looks lined up.
With this van you do not have to prime the fuel filter. Simply turn the key to position 2 for a few seconds. Once you try to start it the van make take a few tries but it will start eventually. I recommend having a friend start the van while you keep an eye on the filter. If something was done wrong (o-ring I referred to above) this will be the time when you notice when a large amount of diesel fuel sprays out onto your engine. If that happens see where it is coming from, shut off the van and tighten or correct the leak. If the fuel comes out the center plastic knob chances are the o-ring inside did not seat properly. Remove the knob completely and check the o-ring. It is plastic so be careful not to break it, it does not have to be tightened that much.