-3deg in July? South America?

"nothing like the muck" might be the key phrase, once you get the glow plug system working. You probably have gotten a batch of water with the fuel, which makes for hard starts due to premature gelling of the fuel. The muck is algae/fungus/little critters that breathe water like we breathe air, and is death for the entire fuel system.

Once you're statisfied the glow system is working, find some biocide and fuel filters. Then look for the tank drain at the bottom of the tank. The idea is to drain the tank from the bottom after you've siphoned or run off (assuming it's running, of course) all but about 5gal from the top, biocide with about 5gal of fresh fuel, let it sit a day or so, drain the tank again, put about 5gal of fresh fuel with an additive like Power Service DieselKleen.

Then change fuel filters. Fill the main filter with 50/50 fuel/DieselKleen. If you have a hand pump then pump for 30 min. If no hand pump you've no choice but to crank with the starter. Change fuel filters again. That should clean out the injector pump and injector nozzle bodies.

Check the air filter and the throttle linkages for anything amiss. Check again for obvious fuel leaks, which means air gets into system and you lose prime. Warm up the engine block with the electric heater or a shallow pan of charcoal under the oil pan. Then try starting engine. If it runs then fill the tank with fresh fuel (with additive) and be prepared to change fuel filters again. If not then you may have blown injector tips. The tips literally blow off due to the erosive nature of the water. Then it's time for an injector rebuild.

Good luck and let's hope it's just the glow plug system. There is no easy or fun way to remove algae, which is why the old timers are clean fuel fanatics.

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daBenz - 1970 220D