Ok, this will be a tad long, but please bear with me. As we know, the basics for combustion in a diesel engine are Fuel, air, compression, and timing, add glow plug heat for starting to that. That said, here is what I would do, and I know some will disagree with me, but this method has worked for me several times in the past.
First and foremost, make SURE all the glow plugs are working. Do a complete test. A good method that has worked for me can be found here
Mercedes Diesel Glow Plug Repair.
Once you know you have good glow plugs, move on to a valve adjustment. Just because compression "feels" ok, does not mean the valves are adjusted correctly. Again, a good valve adjustment method can be found here.
Mercedes Diesel Valve Adjustment Procedure While you are in there you can check the timing chain stretch, and basic timing setting.
Once that is done, change both fuel filters (prefill the spin on filter!), AND check the filter/strainer in the tank for gunk. You can blow some air from a compressor thru the fuel lines to be sure they are clear, then tighten all fuel lines. Lastly replace the hand primer if it is not one of the newer black knob ones.
Unless there is a significant mechanical issue (Burned/broken valve, stuck rings, bad Injection pump, stuck vacuum shut off) it should try to fire. Check the oil level in it, and try cranking it.
One other thing you could do to isolate the fuel system is try to run it off of a separate 5 gallon can of diesel (basically an external tank)
Bottom line is until you know for sure the glow system is working, the valves are adjusted correctly and you have a good fuel supply with clean filters, you will end up spinning your wheels.
Good luck