First of all, one doesn't "clean out" a fuel filter, it's replaced with
a new filter.
Since you opened the fuel system it must be purged of air; this can be
done with the hand primer pump that's probably below the injection pump.
(I don't know this model). Look for what appears to be an 7" x 1.5"
aluminum pipe pointing at you that has a round black plastic top.
Unscrew that top and start pumping to draw fresh fuel into the filter(s)
that were emptied earlier. It should be fine after ten or twenty
strokes, screw the top back on to the hand primer pump.
Then, leave the fuel system alone; that's probably NOT the problem.
Diesels use glow plugs to heat their cold cylinders prior to starting;
that's the light with the coiled wire that's on the dash - it ought to
light for about 10 seconds when the key is turned ON and then go out
signaling the engine is ready to be cranked. There's a glow plug relay
and on it, a metal fuse (fusable link). Chances are that if this is the
first instance of no starting the link is broken cutting the power to
the glow plugs.
The engine won't start without working glow plugs. So you need to
investigate them to ensure they are working. Start by finding the glow
plug relay - trace the wires from the glow plugs - 4 wires on the side
of the head, near the injectors - back to the relay. The glow plug relay
may have a plastic cover over the link. Replacement links are available
from a M-B dealer and others for about $1 or $2 each - your car needs
one - plus a spare.
If you are confident that the glow plugs are working but that there's no
fuel being injected then the next suspects are either an air leak in the
fuel system or that the engine's vacuum powered shut down device no
longer releasing when you want to start the engine. Air leaks are fixed
by being sure all fuel hose connections, filters etc. are secure. The
shut down device is of the "right age" to be suspect. Its a small
bellows that's on or inside the injection pump that pulls the fuel rack
to OFF when you shut down the motor. The bellows wears out, gets oil
logged and fails. Usually the engine doesn't stop and needs to be
stopped by pressing the STOP lever on the throttle linkage.
Diesels are simple motors to maintain. Change the oil, change the
filters and leave them alone.
Hope this helps you.