i have had this 1982 300d for about 5 years now. about 3 weeks ago i could not get it started on a very cold day (<20 degrees F). since then i have done the following.

-replaced the battery
-replaced the glow plugs
-checked for voltage at glow plugs (~11V)
-did a valve adjustment
-permormed a diesel purge
-replace primary and secondary fuel filters
-checked air filter and air intake system for obstruction
-attempted to "prime" the fuel pump (used the hand pump to ensure fuel was hitting the rack before attempting to start.)

i am about to go recheck my valve adjustment and check my fuel injectors for pitting but i figured i would get this post up sooner then later in the hope of getting some knowlage from the community/experts.

IMPORTANT: since that one cold day i have never been able to get the car started WITHOUT 1 or 2 sprays of starting fluid into the air filter housing.

When I use the starting fluid spray the car will start (still hard but it starts) the car then runs rough for about a mile then normal. THE CAR THEN STARTS PERFECTLY as long as it's still warm. Car also starts fine in the morning when i plug in the block heater over night.

Last night it only got down to 36 degrees F here and it was about 45F when i tried starting it. (no block heater no starting fluid) Car wont start.

I'm thinking it's just terminal weak compression at this point but if anyone has any other suggestions please let me know.